src/profiling/perf/event_config.cc - third_party/perfetto - Git at Google

 /*
  * Copyright (C) 2020 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include "src/profiling/perf/event_config.h"

 #include <linux/perf_event.h>
 #include <time.h>

 #include <unwindstack/Regs.h>
 #include <vector>

 #include "perfetto/base/flat_set.h"
 #include "perfetto/ext/base/optional.h"
 #include "perfetto/ext/base/utils.h"
 #include "src/profiling/perf/regs_parsing.h"

 #include "protos/perfetto/common/perf_events.gen.h"
 #include "protos/perfetto/config/profiling/perf_event_config.gen.h"

 namespace perfetto {
 namespace profiling {

 namespace {
 constexpr uint64_t kDefaultSamplingFrequencyHz = 10;
 constexpr uint32_t kDefaultDataPagesPerRingBuffer = 256;  // 1 MB: 256x 4k pages
 constexpr uint32_t kDefaultReadTickPeriodMs = 100;
 constexpr uint32_t kDefaultRemoteDescriptorTimeoutMs = 100;

 // Acceptable forms: "sched/sched_switch" or "sched:sched_switch".
 std::pair<std::string, std::string> SplitTracepointString(
     const std::string& input) {
   auto slash_pos = input.find("/");
   if (slash_pos != std::string::npos)
     return std::make_pair(input.substr(0, slash_pos),
                           input.substr(slash_pos + 1));

   auto colon_pos = input.find(":");
   if (colon_pos != std::string::npos)
     return std::make_pair(input.substr(0, colon_pos),
                           input.substr(colon_pos + 1));

   return std::make_pair("", input);
 }

 // If set, the returned id is guaranteed to be non-zero.
 base::Optional<uint32_t> ParseTracepointAndResolveId(
     const protos::gen::PerfEvents::Tracepoint& tracepoint,
     EventConfig::tracepoint_id_fn_t tracepoint_id_lookup) {
   std::string full_name = tracepoint.name();
   std::string tp_group;
   std::string tp_name;
   std::tie(tp_group, tp_name) = SplitTracepointString(full_name);
   if (tp_group.empty() || tp_name.empty()) {
     PERFETTO_ELOG(
         "Invalid tracepoint format: %s. Should be a full path like "
         "sched:sched_switch or sched/sched_switch.",
         full_name.c_str());
     return base::nullopt;
   }

   uint32_t tracepoint_id = tracepoint_id_lookup(tp_group, tp_name);
   if (!tracepoint_id) {
     PERFETTO_ELOG(
         "Failed to resolve tracepoint %s to its id. Check that tracefs is "
         "accessible and the event exists.",
         full_name.c_str());
     return base::nullopt;
   }
   return base::make_optional(tracepoint_id);
 }

 // |T| is either gen::PerfEventConfig or gen::PerfEventConfig::Scope.
 // Note: the semantics of target_cmdline and exclude_cmdline were changed since
 // their original introduction. They used to be put through a canonicalization
 // function that simplified them to the binary name alone. We no longer do this,
 // regardless of whether we're parsing an old-style config. The overall outcome
 // shouldn't change for almost all existing uses.
 template <typename T>
 TargetFilter ParseTargetFilter(
     const T& cfg,
     base::Optional<ProcessSharding> process_sharding) {
   TargetFilter filter;
   for (const auto& str : cfg.target_cmdline()) {
     filter.cmdlines.push_back(str);
   }
   for (const auto& str : cfg.exclude_cmdline()) {
     filter.exclude_cmdlines.push_back(str);
   }
   for (const int32_t pid : cfg.target_pid()) {
     filter.pids.insert(pid);
   }
   for (const int32_t pid : cfg.exclude_pid()) {
     filter.exclude_pids.insert(pid);
   }
   filter.additional_cmdline_count = cfg.additional_cmdline_count();
   filter.process_sharding = process_sharding;
   return filter;
 }

 constexpr bool IsPowerOfTwo(size_t v) {
   return (v != 0 && ((v & (v - 1)) == 0));
 }

 // returns |base::nullopt| if the input is invalid.
 base::Optional<uint32_t> ChooseActualRingBufferPages(uint32_t config_value) {
   if (!config_value) {
     static_assert(IsPowerOfTwo(kDefaultDataPagesPerRingBuffer), "");
     return base::make_optional(kDefaultDataPagesPerRingBuffer);
   }

   if (!IsPowerOfTwo(config_value)) {
     PERFETTO_ELOG("kernel buffer size must be a power of two pages");
     return base::nullopt;
   }

   return base::make_optional(config_value);
 }

 base::Optional<PerfCounter> ToPerfCounter(
     std::string name,
     protos::gen::PerfEvents::Counter pb_enum) {
   using protos::gen::PerfEvents;
   switch (static_cast<int>(pb_enum)) {  // cast to pacify -Wswitch-enum
     case PerfEvents::SW_CPU_CLOCK:
       return PerfCounter::BuiltinCounter(name, PerfEvents::SW_CPU_CLOCK,
                                          PERF_TYPE_SOFTWARE,
                                          PERF_COUNT_SW_CPU_CLOCK);
     case PerfEvents::SW_PAGE_FAULTS:
       return PerfCounter::BuiltinCounter(name, PerfEvents::SW_PAGE_FAULTS,
                                          PERF_TYPE_SOFTWARE,
                                          PERF_COUNT_SW_PAGE_FAULTS);
     case PerfEvents::SW_TASK_CLOCK:
       return PerfCounter::BuiltinCounter(name, PerfEvents::SW_TASK_CLOCK,
                                          PERF_TYPE_SOFTWARE,
                                          PERF_COUNT_SW_TASK_CLOCK);
     case PerfEvents::SW_CONTEXT_SWITCHES:
       return PerfCounter::BuiltinCounter(name, PerfEvents::SW_CONTEXT_SWITCHES,
                                          PERF_TYPE_SOFTWARE,
                                          PERF_COUNT_SW_CONTEXT_SWITCHES);
     case PerfEvents::SW_CPU_MIGRATIONS:
       return PerfCounter::BuiltinCounter(name, PerfEvents::SW_CPU_MIGRATIONS,
                                          PERF_TYPE_SOFTWARE,
                                          PERF_COUNT_SW_CPU_MIGRATIONS);
     case PerfEvents::SW_PAGE_FAULTS_MIN:
       return PerfCounter::BuiltinCounter(name, PerfEvents::SW_PAGE_FAULTS_MIN,
                                          PERF_TYPE_SOFTWARE,
                                          PERF_COUNT_SW_PAGE_FAULTS_MIN);
     case PerfEvents::SW_PAGE_FAULTS_MAJ:
       return PerfCounter::BuiltinCounter(name, PerfEvents::SW_PAGE_FAULTS_MAJ,
                                          PERF_TYPE_SOFTWARE,
                                          PERF_COUNT_SW_PAGE_FAULTS_MAJ);
     case PerfEvents::SW_ALIGNMENT_FAULTS:
       return PerfCounter::BuiltinCounter(name, PerfEvents::SW_ALIGNMENT_FAULTS,
                                          PERF_TYPE_SOFTWARE,
                                          PERF_COUNT_SW_ALIGNMENT_FAULTS);
     case PerfEvents::SW_EMULATION_FAULTS:
       return PerfCounter::BuiltinCounter(name, PerfEvents::SW_EMULATION_FAULTS,
                                          PERF_TYPE_SOFTWARE,
                                          PERF_COUNT_SW_EMULATION_FAULTS);
     case PerfEvents::SW_DUMMY:
       return PerfCounter::BuiltinCounter(
           name, PerfEvents::SW_DUMMY, PERF_TYPE_SOFTWARE, PERF_COUNT_SW_DUMMY);

     case PerfEvents::HW_CPU_CYCLES:
       return PerfCounter::BuiltinCounter(name, PerfEvents::HW_CPU_CYCLES,
                                          PERF_TYPE_HARDWARE,
                                          PERF_COUNT_HW_CPU_CYCLES);
     case PerfEvents::HW_INSTRUCTIONS:
       return PerfCounter::BuiltinCounter(name, PerfEvents::HW_INSTRUCTIONS,
                                          PERF_TYPE_HARDWARE,
                                          PERF_COUNT_HW_INSTRUCTIONS);
     case PerfEvents::HW_CACHE_REFERENCES:
       return PerfCounter::BuiltinCounter(name, PerfEvents::HW_CACHE_REFERENCES,
                                          PERF_TYPE_HARDWARE,
                                          PERF_COUNT_HW_CACHE_REFERENCES);
     case PerfEvents::HW_CACHE_MISSES:
       return PerfCounter::BuiltinCounter(name, PerfEvents::HW_CACHE_MISSES,
                                          PERF_TYPE_HARDWARE,
                                          PERF_COUNT_HW_CACHE_MISSES);
     case PerfEvents::HW_BRANCH_INSTRUCTIONS:
       return PerfCounter::BuiltinCounter(
           name, PerfEvents::HW_BRANCH_INSTRUCTIONS, PERF_TYPE_HARDWARE,
           PERF_COUNT_HW_BRANCH_INSTRUCTIONS);
     case PerfEvents::HW_BRANCH_MISSES:
       return PerfCounter::BuiltinCounter(name, PerfEvents::HW_BRANCH_MISSES,
                                          PERF_TYPE_HARDWARE,
                                          PERF_COUNT_HW_BRANCH_MISSES);
     case PerfEvents::HW_BUS_CYCLES:
       return PerfCounter::BuiltinCounter(name, PerfEvents::HW_BUS_CYCLES,
                                          PERF_TYPE_HARDWARE,
                                          PERF_COUNT_HW_BUS_CYCLES);
     case PerfEvents::HW_STALLED_CYCLES_FRONTEND:
       return PerfCounter::BuiltinCounter(
           name, PerfEvents::HW_STALLED_CYCLES_FRONTEND, PERF_TYPE_HARDWARE,
           PERF_COUNT_HW_STALLED_CYCLES_FRONTEND);
     case PerfEvents::HW_STALLED_CYCLES_BACKEND:
       return PerfCounter::BuiltinCounter(
           name, PerfEvents::HW_STALLED_CYCLES_BACKEND, PERF_TYPE_HARDWARE,
           PERF_COUNT_HW_STALLED_CYCLES_BACKEND);
     case PerfEvents::HW_REF_CPU_CYCLES:
       return PerfCounter::BuiltinCounter(name, PerfEvents::HW_REF_CPU_CYCLES,
                                          PERF_TYPE_HARDWARE,
                                          PERF_COUNT_HW_REF_CPU_CYCLES);

     default:
       PERFETTO_ELOG("Unrecognised PerfEvents::Counter enum value: %zu",
                     static_cast<size_t>(pb_enum));
       return base::nullopt;
   }
 }

 int32_t ToClockId(protos::gen::PerfEvents::PerfClock pb_enum) {
   using protos::gen::PerfEvents;
   switch (static_cast<int>(pb_enum)) {  // cast to pacify -Wswitch-enum
     case PerfEvents::PERF_CLOCK_REALTIME:
       return CLOCK_REALTIME;
     case PerfEvents::PERF_CLOCK_MONOTONIC:
       return CLOCK_MONOTONIC;
     case PerfEvents::PERF_CLOCK_MONOTONIC_RAW:
       return CLOCK_MONOTONIC_RAW;
     case PerfEvents::PERF_CLOCK_BOOTTIME:
       return CLOCK_BOOTTIME;
     // Default to a monotonic clock since it should be compatible with all types
     // of events. Whereas boottime cannot be used with hardware events due to
     // potential access within non-maskable interrupts.
     default:
       return CLOCK_MONOTONIC_RAW;
   }
 }

 }  // namespace

 // static
 PerfCounter PerfCounter::BuiltinCounter(
     std::string name,
     protos::gen::PerfEvents::Counter counter,
     uint32_t type,
     uint64_t config) {
   PerfCounter ret;
   ret.type = PerfCounter::Type::kBuiltinCounter;
   ret.counter = counter;
   ret.name = std::move(name);

   ret.attr_type = type;
   ret.attr_config = config;
   // none of the builtin counters require config1 and config2 at the moment
   return ret;
 }

 // static
 PerfCounter PerfCounter::Tracepoint(std::string name,
                                     std::string tracepoint_name,
                                     std::string tracepoint_filter,
                                     uint64_t id) {
   PerfCounter ret;
   ret.type = PerfCounter::Type::kTracepoint;
   ret.tracepoint_name = std::move(tracepoint_name);
   ret.tracepoint_filter = std::move(tracepoint_filter);
   ret.name = std::move(name);

   ret.attr_type = PERF_TYPE_TRACEPOINT;
   ret.attr_config = id;
   return ret;
 }

 // static
 PerfCounter PerfCounter::RawEvent(std::string name,
                                   uint32_t type,
                                   uint64_t config,
                                   uint64_t config1,
                                   uint64_t config2) {
   PerfCounter ret;
   ret.type = PerfCounter::Type::kRawEvent;
   ret.name = std::move(name);

   ret.attr_type = type;
   ret.attr_config = config;
   ret.attr_config1 = config1;
   ret.attr_config2 = config2;
   return ret;
 }

 // static
 base::Optional<EventConfig> EventConfig::Create(
     const protos::gen::PerfEventConfig& pb_config,
     const DataSourceConfig& raw_ds_config,
     base::Optional<ProcessSharding> process_sharding,
     tracepoint_id_fn_t tracepoint_id_lookup) {
   // Timebase: sampling interval.
   uint64_t sampling_frequency = 0;
   uint64_t sampling_period = 0;
   if (pb_config.timebase().period()) {
     sampling_period = pb_config.timebase().period();
   } else if (pb_config.timebase().frequency()) {
     sampling_frequency = pb_config.timebase().frequency();
   } else if (pb_config.sampling_frequency()) {  // backwards compatibility
     sampling_frequency = pb_config.sampling_frequency();
   } else {
     sampling_frequency = kDefaultSamplingFrequencyHz;
   }
   PERFETTO_DCHECK(sampling_period && !sampling_frequency ||
                   !sampling_period && sampling_frequency);

   // Timebase event. Default: CPU timer.
   PerfCounter timebase_event;
   std::string timebase_name = pb_config.timebase().name();
   if (pb_config.timebase().has_counter()) {
     auto maybe_counter =
         ToPerfCounter(timebase_name, pb_config.timebase().counter());
     if (!maybe_counter)
       return base::nullopt;
     timebase_event = *maybe_counter;

   } else if (pb_config.timebase().has_tracepoint()) {
     const auto& tracepoint_pb = pb_config.timebase().tracepoint();
     base::Optional<uint32_t> maybe_id =
         ParseTracepointAndResolveId(tracepoint_pb, tracepoint_id_lookup);
     if (!maybe_id)
       return base::nullopt;
     timebase_event = PerfCounter::Tracepoint(
         timebase_name, tracepoint_pb.name(), tracepoint_pb.filter(), *maybe_id);

   } else if (pb_config.timebase().has_raw_event()) {
     const auto& raw = pb_config.timebase().raw_event();
     timebase_event = PerfCounter::RawEvent(
         timebase_name, raw.type(), raw.config(), raw.config1(), raw.config2());

   } else {
     timebase_event = PerfCounter::BuiltinCounter(
         timebase_name, protos::gen::PerfEvents::PerfEvents::SW_CPU_CLOCK,
         PERF_TYPE_SOFTWARE, PERF_COUNT_SW_CPU_CLOCK);
   }

   // Callstack sampling.
   bool user_frames = false;
   bool kernel_frames = false;
   TargetFilter target_filter;
   bool legacy_config = pb_config.all_cpus();  // all_cpus was mandatory before
   if (pb_config.has_callstack_sampling() || legacy_config) {
     user_frames = true;

     // Userspace callstacks.
     using protos::gen::PerfEventConfig;
     switch (static_cast<int>(pb_config.callstack_sampling().user_frames())) {
       case PerfEventConfig::UNWIND_UNKNOWN:
         // default to true, both for backwards compatibility and because it's
         // almost always what the user wants.
         user_frames = true;
         break;
       case PerfEventConfig::UNWIND_SKIP:
         user_frames = false;
         break;
       case PerfEventConfig::UNWIND_DWARF:
         user_frames = true;
         break;
       default:
         // enum value from the future that we don't yet know, refuse the config
         // TODO(rsavitski): double-check that both pbzero and ::gen propagate
         // unknown enum values.
         return base::nullopt;
     }

     // Process scoping. Sharding parameter is supplied from outside as it is
     // shared by all data sources within a tracing session.
     target_filter =
         pb_config.callstack_sampling().has_scope()
             ? ParseTargetFilter(pb_config.callstack_sampling().scope(),
                                 process_sharding)
             : ParseTargetFilter(pb_config,
                                 process_sharding);  // backwards compatibility

     // Kernel callstacks.
     kernel_frames = pb_config.callstack_sampling().kernel_frames() ||
                     pb_config.kernel_frames();
   }

   // Ring buffer options.
   base::Optional<uint32_t> ring_buffer_pages =
       ChooseActualRingBufferPages(pb_config.ring_buffer_pages());
   if (!ring_buffer_pages.has_value())
     return base::nullopt;

   uint32_t read_tick_period_ms = pb_config.ring_buffer_read_period_ms()
                                      ? pb_config.ring_buffer_read_period_ms()
                                      : kDefaultReadTickPeriodMs;

   // Calculate a rough upper limit for the amount of samples the producer
   // should read per read tick, as a safeguard against getting stuck chasing the
   // ring buffer head indefinitely.
   uint64_t samples_per_tick_limit = 0;
   if (sampling_frequency) {
     // expected = rate * period, with a conversion of period from ms to s:
     uint64_t expected_samples_per_tick =
         1 + (sampling_frequency * read_tick_period_ms) / 1000;
     // Double the limit to account of actual sample rate uncertainties, as
     // well as any other factors:
     samples_per_tick_limit = 2 * expected_samples_per_tick;
   } else {  // sampling_period
     // We don't know the sample rate that a fixed period would cause, but we can
     // still estimate how many samples will fit in one pass of the ring buffer
     // (with the assumption that we don't want to read more than one buffer's
     // capacity within a tick).
     // TODO(rsavitski): for now, make an extremely conservative guess of an 8
     // byte sample (stack sampling samples can be up to 64KB). This is most
     // likely as good as no limit in practice.
     samples_per_tick_limit = *ring_buffer_pages * (base::kPageSize / 8);
   }
   PERFETTO_DLOG("Capping samples (not records) per tick to [%" PRIu64 "]",
                 samples_per_tick_limit);
   if (samples_per_tick_limit == 0)
     return base::nullopt;

   // Optional footprint controls.
   uint64_t max_enqueued_footprint_bytes =
       pb_config.max_enqueued_footprint_kb() * 1024;

   // Android-specific options.
   uint32_t remote_descriptor_timeout_ms =
       pb_config.remote_descriptor_timeout_ms()
           ? pb_config.remote_descriptor_timeout_ms()
           : kDefaultRemoteDescriptorTimeoutMs;

   // Build the underlying syscall config struct.
   perf_event_attr pe = {};
   pe.size = sizeof(perf_event_attr);
   pe.disabled = 1;  // will be activated via ioctl

   // Sampling timebase.
   pe.type = timebase_event.attr_type;
   pe.config = timebase_event.attr_config;
   pe.config1 = timebase_event.attr_config1;
   pe.config2 = timebase_event.attr_config2;
   if (sampling_frequency) {
     pe.freq = true;
     pe.sample_freq = sampling_frequency;
   } else {
     pe.sample_period = sampling_period;
   }

   // What the samples will contain.
   pe.sample_type = PERF_SAMPLE_TID | PERF_SAMPLE_TIME | PERF_SAMPLE_READ;
   // PERF_SAMPLE_TIME:
   pe.clockid = ToClockId(pb_config.timebase().timestamp_clock());
   pe.use_clockid = true;

   if (user_frames) {
     pe.sample_type |= PERF_SAMPLE_STACK_USER | PERF_SAMPLE_REGS_USER;
     // PERF_SAMPLE_STACK_USER:
     // Needs to be < ((u16)(~0u)), and have bottom 8 bits clear.
     // Note that the kernel still needs to make space for the other parts of the
     // sample (up to the max record size of 64k), so the effective maximum
     // can be lower than this.
     pe.sample_stack_user = (1u << 16) - 256;
     // PERF_SAMPLE_REGS_USER:
     pe.sample_regs_user =
         PerfUserRegsMaskForArch(unwindstack::Regs::CurrentArch());
   }
   if (kernel_frames) {
     pe.sample_type |= PERF_SAMPLE_CALLCHAIN;
     pe.exclude_callchain_user = true;
   }

   return EventConfig(
       raw_ds_config, pe, timebase_event, user_frames, kernel_frames,
       std::move(target_filter), ring_buffer_pages.value(), read_tick_period_ms,
       samples_per_tick_limit, remote_descriptor_timeout_ms,
       pb_config.unwind_state_clear_period_ms(), max_enqueued_footprint_bytes,
       pb_config.target_installed_by());
 }

 EventConfig::EventConfig(const DataSourceConfig& raw_ds_config,
                          const perf_event_attr& pe,
                          const PerfCounter& timebase_event,
                          bool user_frames,
                          bool kernel_frames,
                          TargetFilter target_filter,
                          uint32_t ring_buffer_pages,
                          uint32_t read_tick_period_ms,
                          uint64_t samples_per_tick_limit,
                          uint32_t remote_descriptor_timeout_ms,
                          uint32_t unwind_state_clear_period_ms,
                          uint64_t max_enqueued_footprint_bytes,
                          std::vector<std::string> target_installed_by)
     : perf_event_attr_(pe),
       timebase_event_(timebase_event),
       user_frames_(user_frames),
       kernel_frames_(kernel_frames),
       target_filter_(std::move(target_filter)),
       ring_buffer_pages_(ring_buffer_pages),
       read_tick_period_ms_(read_tick_period_ms),
       samples_per_tick_limit_(samples_per_tick_limit),
       remote_descriptor_timeout_ms_(remote_descriptor_timeout_ms),
       unwind_state_clear_period_ms_(unwind_state_clear_period_ms),
       max_enqueued_footprint_bytes_(max_enqueued_footprint_bytes),
       target_installed_by_(std::move(target_installed_by)),
       raw_ds_config_(raw_ds_config) /* full copy */ {}

 }  // namespace profiling
 }  // namespace perfetto
	/*
	* Copyright (C) 2020 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include "src/profiling/perf/event_config.h"

	#include <linux/perf_event.h>
	#include <time.h>

	#include <unwindstack/Regs.h>
	#include <vector>

	#include "perfetto/base/flat_set.h"
	#include "perfetto/ext/base/optional.h"
	#include "perfetto/ext/base/utils.h"
	#include "src/profiling/perf/regs_parsing.h"

	#include "protos/perfetto/common/perf_events.gen.h"
	#include "protos/perfetto/config/profiling/perf_event_config.gen.h"

	namespace perfetto {
	namespace profiling {

	namespace {
	constexpr uint64_t kDefaultSamplingFrequencyHz = 10;
	constexpr uint32_t kDefaultDataPagesPerRingBuffer = 256; // 1 MB: 256x 4k pages
	constexpr uint32_t kDefaultReadTickPeriodMs = 100;
	constexpr uint32_t kDefaultRemoteDescriptorTimeoutMs = 100;

	// Acceptable forms: "sched/sched_switch" or "sched:sched_switch".
	std::pair<std::string, std::string> SplitTracepointString(
	const std::string& input) {
	auto slash_pos = input.find("/");
	if (slash_pos != std::string::npos)
	return std::make_pair(input.substr(0, slash_pos),
	input.substr(slash_pos + 1));

	auto colon_pos = input.find(":");
	if (colon_pos != std::string::npos)
	return std::make_pair(input.substr(0, colon_pos),
	input.substr(colon_pos + 1));

	return std::make_pair("", input);
	}

	// If set, the returned id is guaranteed to be non-zero.
	base::Optional<uint32_t> ParseTracepointAndResolveId(
	const protos::gen::PerfEvents::Tracepoint& tracepoint,
	EventConfig::tracepoint_id_fn_t tracepoint_id_lookup) {
	std::string full_name = tracepoint.name();
	std::string tp_group;
	std::string tp_name;
	std::tie(tp_group, tp_name) = SplitTracepointString(full_name);
	if (tp_group.empty() \|\| tp_name.empty()) {
	PERFETTO_ELOG(
	"Invalid tracepoint format: %s. Should be a full path like "
	"sched:sched_switch or sched/sched_switch.",
	full_name.c_str());
	return base::nullopt;
	}

	uint32_t tracepoint_id = tracepoint_id_lookup(tp_group, tp_name);
	if (!tracepoint_id) {
	PERFETTO_ELOG(
	"Failed to resolve tracepoint %s to its id. Check that tracefs is "
	"accessible and the event exists.",
	full_name.c_str());
	return base::nullopt;
	}
	return base::make_optional(tracepoint_id);
	}

	// \|T\| is either gen::PerfEventConfig or gen::PerfEventConfig::Scope.
	// Note: the semantics of target_cmdline and exclude_cmdline were changed since
	// their original introduction. They used to be put through a canonicalization
	// function that simplified them to the binary name alone. We no longer do this,
	// regardless of whether we're parsing an old-style config. The overall outcome
	// shouldn't change for almost all existing uses.
	template <typename T>
	TargetFilter ParseTargetFilter(
	const T& cfg,
	base::Optional<ProcessSharding> process_sharding) {
	TargetFilter filter;
	for (const auto& str : cfg.target_cmdline()) {
	filter.cmdlines.push_back(str);
	}
	for (const auto& str : cfg.exclude_cmdline()) {
	filter.exclude_cmdlines.push_back(str);
	}
	for (const int32_t pid : cfg.target_pid()) {
	filter.pids.insert(pid);
	}
	for (const int32_t pid : cfg.exclude_pid()) {
	filter.exclude_pids.insert(pid);
	}
	filter.additional_cmdline_count = cfg.additional_cmdline_count();
	filter.process_sharding = process_sharding;
	return filter;
	}

	constexpr bool IsPowerOfTwo(size_t v) {
	return (v != 0 && ((v & (v - 1)) == 0));
	}

	// returns \|base::nullopt\| if the input is invalid.
	base::Optional<uint32_t> ChooseActualRingBufferPages(uint32_t config_value) {
	if (!config_value) {
	static_assert(IsPowerOfTwo(kDefaultDataPagesPerRingBuffer), "");
	return base::make_optional(kDefaultDataPagesPerRingBuffer);
	}

	if (!IsPowerOfTwo(config_value)) {
	PERFETTO_ELOG("kernel buffer size must be a power of two pages");
	return base::nullopt;
	}

	return base::make_optional(config_value);
	}

	base::Optional<PerfCounter> ToPerfCounter(
	std::string name,
	protos::gen::PerfEvents::Counter pb_enum) {
	using protos::gen::PerfEvents;
	switch (static_cast<int>(pb_enum)) { // cast to pacify -Wswitch-enum
	case PerfEvents::SW_CPU_CLOCK:
	return PerfCounter::BuiltinCounter(name, PerfEvents::SW_CPU_CLOCK,
	PERF_TYPE_SOFTWARE,
	PERF_COUNT_SW_CPU_CLOCK);
	case PerfEvents::SW_PAGE_FAULTS:
	return PerfCounter::BuiltinCounter(name, PerfEvents::SW_PAGE_FAULTS,
	PERF_TYPE_SOFTWARE,
	PERF_COUNT_SW_PAGE_FAULTS);
	case PerfEvents::SW_TASK_CLOCK:
	return PerfCounter::BuiltinCounter(name, PerfEvents::SW_TASK_CLOCK,
	PERF_TYPE_SOFTWARE,
	PERF_COUNT_SW_TASK_CLOCK);
	case PerfEvents::SW_CONTEXT_SWITCHES:
	return PerfCounter::BuiltinCounter(name, PerfEvents::SW_CONTEXT_SWITCHES,
	PERF_TYPE_SOFTWARE,
	PERF_COUNT_SW_CONTEXT_SWITCHES);
	case PerfEvents::SW_CPU_MIGRATIONS:
	return PerfCounter::BuiltinCounter(name, PerfEvents::SW_CPU_MIGRATIONS,
	PERF_TYPE_SOFTWARE,
	PERF_COUNT_SW_CPU_MIGRATIONS);
	case PerfEvents::SW_PAGE_FAULTS_MIN:
	return PerfCounter::BuiltinCounter(name, PerfEvents::SW_PAGE_FAULTS_MIN,
	PERF_TYPE_SOFTWARE,
	PERF_COUNT_SW_PAGE_FAULTS_MIN);
	case PerfEvents::SW_PAGE_FAULTS_MAJ:
	return PerfCounter::BuiltinCounter(name, PerfEvents::SW_PAGE_FAULTS_MAJ,
	PERF_TYPE_SOFTWARE,
	PERF_COUNT_SW_PAGE_FAULTS_MAJ);
	case PerfEvents::SW_ALIGNMENT_FAULTS:
	return PerfCounter::BuiltinCounter(name, PerfEvents::SW_ALIGNMENT_FAULTS,
	PERF_TYPE_SOFTWARE,
	PERF_COUNT_SW_ALIGNMENT_FAULTS);
	case PerfEvents::SW_EMULATION_FAULTS:
	return PerfCounter::BuiltinCounter(name, PerfEvents::SW_EMULATION_FAULTS,
	PERF_TYPE_SOFTWARE,
	PERF_COUNT_SW_EMULATION_FAULTS);
	case PerfEvents::SW_DUMMY:
	return PerfCounter::BuiltinCounter(
	name, PerfEvents::SW_DUMMY, PERF_TYPE_SOFTWARE, PERF_COUNT_SW_DUMMY);

	case PerfEvents::HW_CPU_CYCLES:
	return PerfCounter::BuiltinCounter(name, PerfEvents::HW_CPU_CYCLES,
	PERF_TYPE_HARDWARE,
	PERF_COUNT_HW_CPU_CYCLES);
	case PerfEvents::HW_INSTRUCTIONS:
	return PerfCounter::BuiltinCounter(name, PerfEvents::HW_INSTRUCTIONS,
	PERF_TYPE_HARDWARE,
	PERF_COUNT_HW_INSTRUCTIONS);
	case PerfEvents::HW_CACHE_REFERENCES:
	return PerfCounter::BuiltinCounter(name, PerfEvents::HW_CACHE_REFERENCES,
	PERF_TYPE_HARDWARE,
	PERF_COUNT_HW_CACHE_REFERENCES);
	case PerfEvents::HW_CACHE_MISSES:
	return PerfCounter::BuiltinCounter(name, PerfEvents::HW_CACHE_MISSES,
	PERF_TYPE_HARDWARE,
	PERF_COUNT_HW_CACHE_MISSES);
	case PerfEvents::HW_BRANCH_INSTRUCTIONS:
	return PerfCounter::BuiltinCounter(
	name, PerfEvents::HW_BRANCH_INSTRUCTIONS, PERF_TYPE_HARDWARE,
	PERF_COUNT_HW_BRANCH_INSTRUCTIONS);
	case PerfEvents::HW_BRANCH_MISSES:
	return PerfCounter::BuiltinCounter(name, PerfEvents::HW_BRANCH_MISSES,
	PERF_TYPE_HARDWARE,
	PERF_COUNT_HW_BRANCH_MISSES);
	case PerfEvents::HW_BUS_CYCLES:
	return PerfCounter::BuiltinCounter(name, PerfEvents::HW_BUS_CYCLES,
	PERF_TYPE_HARDWARE,
	PERF_COUNT_HW_BUS_CYCLES);
	case PerfEvents::HW_STALLED_CYCLES_FRONTEND:
	return PerfCounter::BuiltinCounter(
	name, PerfEvents::HW_STALLED_CYCLES_FRONTEND, PERF_TYPE_HARDWARE,
	PERF_COUNT_HW_STALLED_CYCLES_FRONTEND);
	case PerfEvents::HW_STALLED_CYCLES_BACKEND:
	return PerfCounter::BuiltinCounter(
	name, PerfEvents::HW_STALLED_CYCLES_BACKEND, PERF_TYPE_HARDWARE,
	PERF_COUNT_HW_STALLED_CYCLES_BACKEND);
	case PerfEvents::HW_REF_CPU_CYCLES:
	return PerfCounter::BuiltinCounter(name, PerfEvents::HW_REF_CPU_CYCLES,
	PERF_TYPE_HARDWARE,
	PERF_COUNT_HW_REF_CPU_CYCLES);

	default:
	PERFETTO_ELOG("Unrecognised PerfEvents::Counter enum value: %zu",
	static_cast<size_t>(pb_enum));
	return base::nullopt;
	}
	}

	int32_t ToClockId(protos::gen::PerfEvents::PerfClock pb_enum) {
	using protos::gen::PerfEvents;
	switch (static_cast<int>(pb_enum)) { // cast to pacify -Wswitch-enum
	case PerfEvents::PERF_CLOCK_REALTIME:
	return CLOCK_REALTIME;
	case PerfEvents::PERF_CLOCK_MONOTONIC:
	return CLOCK_MONOTONIC;
	case PerfEvents::PERF_CLOCK_MONOTONIC_RAW:
	return CLOCK_MONOTONIC_RAW;
	case PerfEvents::PERF_CLOCK_BOOTTIME:
	return CLOCK_BOOTTIME;
	// Default to a monotonic clock since it should be compatible with all types
	// of events. Whereas boottime cannot be used with hardware events due to
	// potential access within non-maskable interrupts.
	default:
	return CLOCK_MONOTONIC_RAW;
	}
	}

	} // namespace

	// static
	PerfCounter PerfCounter::BuiltinCounter(
	std::string name,
	protos::gen::PerfEvents::Counter counter,
	uint32_t type,
	uint64_t config) {
	PerfCounter ret;
	ret.type = PerfCounter::Type::kBuiltinCounter;
	ret.counter = counter;
	ret.name = std::move(name);

	ret.attr_type = type;
	ret.attr_config = config;
	// none of the builtin counters require config1 and config2 at the moment
	return ret;
	}

	// static
	PerfCounter PerfCounter::Tracepoint(std::string name,
	std::string tracepoint_name,
	std::string tracepoint_filter,
	uint64_t id) {
	PerfCounter ret;
	ret.type = PerfCounter::Type::kTracepoint;
	ret.tracepoint_name = std::move(tracepoint_name);
	ret.tracepoint_filter = std::move(tracepoint_filter);
	ret.name = std::move(name);

	ret.attr_type = PERF_TYPE_TRACEPOINT;
	ret.attr_config = id;
	return ret;
	}

	// static
	PerfCounter PerfCounter::RawEvent(std::string name,
	uint32_t type,
	uint64_t config,
	uint64_t config1,
	uint64_t config2) {
	PerfCounter ret;
	ret.type = PerfCounter::Type::kRawEvent;
	ret.name = std::move(name);

	ret.attr_type = type;
	ret.attr_config = config;
	ret.attr_config1 = config1;
	ret.attr_config2 = config2;
	return ret;
	}

	// static
	base::Optional<EventConfig> EventConfig::Create(
	const protos::gen::PerfEventConfig& pb_config,
	const DataSourceConfig& raw_ds_config,
	base::Optional<ProcessSharding> process_sharding,
	tracepoint_id_fn_t tracepoint_id_lookup) {
	// Timebase: sampling interval.
	uint64_t sampling_frequency = 0;
	uint64_t sampling_period = 0;
	if (pb_config.timebase().period()) {
	sampling_period = pb_config.timebase().period();
	} else if (pb_config.timebase().frequency()) {
	sampling_frequency = pb_config.timebase().frequency();
	} else if (pb_config.sampling_frequency()) { // backwards compatibility
	sampling_frequency = pb_config.sampling_frequency();
	} else {
	sampling_frequency = kDefaultSamplingFrequencyHz;
	}
	PERFETTO_DCHECK(sampling_period && !sampling_frequency \|\|
	!sampling_period && sampling_frequency);

	// Timebase event. Default: CPU timer.
	PerfCounter timebase_event;
	std::string timebase_name = pb_config.timebase().name();
	if (pb_config.timebase().has_counter()) {
	auto maybe_counter =
	ToPerfCounter(timebase_name, pb_config.timebase().counter());
	if (!maybe_counter)
	return base::nullopt;
	timebase_event = *maybe_counter;

	} else if (pb_config.timebase().has_tracepoint()) {
	const auto& tracepoint_pb = pb_config.timebase().tracepoint();
	base::Optional<uint32_t> maybe_id =
	ParseTracepointAndResolveId(tracepoint_pb, tracepoint_id_lookup);
	if (!maybe_id)
	return base::nullopt;
	timebase_event = PerfCounter::Tracepoint(
	timebase_name, tracepoint_pb.name(), tracepoint_pb.filter(), *maybe_id);

	} else if (pb_config.timebase().has_raw_event()) {
	const auto& raw = pb_config.timebase().raw_event();
	timebase_event = PerfCounter::RawEvent(
	timebase_name, raw.type(), raw.config(), raw.config1(), raw.config2());

	} else {
	timebase_event = PerfCounter::BuiltinCounter(
	timebase_name, protos::gen::PerfEvents::PerfEvents::SW_CPU_CLOCK,
	PERF_TYPE_SOFTWARE, PERF_COUNT_SW_CPU_CLOCK);
	}

	// Callstack sampling.
	bool user_frames = false;
	bool kernel_frames = false;
	TargetFilter target_filter;
	bool legacy_config = pb_config.all_cpus(); // all_cpus was mandatory before
	if (pb_config.has_callstack_sampling() \|\| legacy_config) {
	user_frames = true;

	// Userspace callstacks.
	using protos::gen::PerfEventConfig;
	switch (static_cast<int>(pb_config.callstack_sampling().user_frames())) {
	case PerfEventConfig::UNWIND_UNKNOWN:
	// default to true, both for backwards compatibility and because it's
	// almost always what the user wants.
	user_frames = true;
	break;
	case PerfEventConfig::UNWIND_SKIP:
	user_frames = false;
	break;
	case PerfEventConfig::UNWIND_DWARF:
	user_frames = true;
	break;
	default:
	// enum value from the future that we don't yet know, refuse the config
	// TODO(rsavitski): double-check that both pbzero and ::gen propagate
	// unknown enum values.
	return base::nullopt;
	}

	// Process scoping. Sharding parameter is supplied from outside as it is
	// shared by all data sources within a tracing session.
	target_filter =
	pb_config.callstack_sampling().has_scope()
	? ParseTargetFilter(pb_config.callstack_sampling().scope(),
	process_sharding)
	: ParseTargetFilter(pb_config,
	process_sharding); // backwards compatibility

	// Kernel callstacks.
	kernel_frames = pb_config.callstack_sampling().kernel_frames() \|\|
	pb_config.kernel_frames();
	}

	// Ring buffer options.
	base::Optional<uint32_t> ring_buffer_pages =
	ChooseActualRingBufferPages(pb_config.ring_buffer_pages());
	if (!ring_buffer_pages.has_value())
	return base::nullopt;

	uint32_t read_tick_period_ms = pb_config.ring_buffer_read_period_ms()
	? pb_config.ring_buffer_read_period_ms()
	: kDefaultReadTickPeriodMs;

	// Calculate a rough upper limit for the amount of samples the producer
	// should read per read tick, as a safeguard against getting stuck chasing the
	// ring buffer head indefinitely.
	uint64_t samples_per_tick_limit = 0;
	if (sampling_frequency) {
	// expected = rate * period, with a conversion of period from ms to s:
	uint64_t expected_samples_per_tick =
	1 + (sampling_frequency * read_tick_period_ms) / 1000;
	// Double the limit to account of actual sample rate uncertainties, as
	// well as any other factors:
	samples_per_tick_limit = 2 * expected_samples_per_tick;
	} else { // sampling_period
	// We don't know the sample rate that a fixed period would cause, but we can
	// still estimate how many samples will fit in one pass of the ring buffer
	// (with the assumption that we don't want to read more than one buffer's
	// capacity within a tick).
	// TODO(rsavitski): for now, make an extremely conservative guess of an 8
	// byte sample (stack sampling samples can be up to 64KB). This is most
	// likely as good as no limit in practice.
	samples_per_tick_limit = ring_buffer_pages (base::kPageSize / 8);
	}
	PERFETTO_DLOG("Capping samples (not records) per tick to [%" PRIu64 "]",
	samples_per_tick_limit);
	if (samples_per_tick_limit == 0)
	return base::nullopt;

	// Optional footprint controls.
	uint64_t max_enqueued_footprint_bytes =
	pb_config.max_enqueued_footprint_kb() * 1024;

	// Android-specific options.
	uint32_t remote_descriptor_timeout_ms =
	pb_config.remote_descriptor_timeout_ms()
	? pb_config.remote_descriptor_timeout_ms()
	: kDefaultRemoteDescriptorTimeoutMs;

	// Build the underlying syscall config struct.
	perf_event_attr pe = {};
	pe.size = sizeof(perf_event_attr);
	pe.disabled = 1; // will be activated via ioctl

	// Sampling timebase.
	pe.type = timebase_event.attr_type;
	pe.config = timebase_event.attr_config;
	pe.config1 = timebase_event.attr_config1;
	pe.config2 = timebase_event.attr_config2;
	if (sampling_frequency) {
	pe.freq = true;
	pe.sample_freq = sampling_frequency;
	} else {
	pe.sample_period = sampling_period;
	}

	// What the samples will contain.
	pe.sample_type = PERF_SAMPLE_TID \| PERF_SAMPLE_TIME \| PERF_SAMPLE_READ;
	// PERF_SAMPLE_TIME:
	pe.clockid = ToClockId(pb_config.timebase().timestamp_clock());
	pe.use_clockid = true;

	if (user_frames) {
	pe.sample_type \|= PERF_SAMPLE_STACK_USER \| PERF_SAMPLE_REGS_USER;
	// PERF_SAMPLE_STACK_USER:
	// Needs to be < ((u16)(~0u)), and have bottom 8 bits clear.
	// Note that the kernel still needs to make space for the other parts of the
	// sample (up to the max record size of 64k), so the effective maximum
	// can be lower than this.
	pe.sample_stack_user = (1u << 16) - 256;
	// PERF_SAMPLE_REGS_USER:
	pe.sample_regs_user =
	PerfUserRegsMaskForArch(unwindstack::Regs::CurrentArch());
	}
	if (kernel_frames) {
	pe.sample_type \|= PERF_SAMPLE_CALLCHAIN;
	pe.exclude_callchain_user = true;
	}

	return EventConfig(
	raw_ds_config, pe, timebase_event, user_frames, kernel_frames,
	std::move(target_filter), ring_buffer_pages.value(), read_tick_period_ms,
	samples_per_tick_limit, remote_descriptor_timeout_ms,
	pb_config.unwind_state_clear_period_ms(), max_enqueued_footprint_bytes,
	pb_config.target_installed_by());
	}

	EventConfig::EventConfig(const DataSourceConfig& raw_ds_config,
	const perf_event_attr& pe,
	const PerfCounter& timebase_event,
	bool user_frames,
	bool kernel_frames,
	TargetFilter target_filter,
	uint32_t ring_buffer_pages,
	uint32_t read_tick_period_ms,
	uint64_t samples_per_tick_limit,
	uint32_t remote_descriptor_timeout_ms,
	uint32_t unwind_state_clear_period_ms,
	uint64_t max_enqueued_footprint_bytes,
	std::vector<std::string> target_installed_by)
	: perf_event_attr_(pe),
	timebase_event_(timebase_event),
	user_frames_(user_frames),
	kernel_frames_(kernel_frames),
	target_filter_(std::move(target_filter)),
	ring_buffer_pages_(ring_buffer_pages),
	read_tick_period_ms_(read_tick_period_ms),
	samples_per_tick_limit_(samples_per_tick_limit),
	remote_descriptor_timeout_ms_(remote_descriptor_timeout_ms),
	unwind_state_clear_period_ms_(unwind_state_clear_period_ms),
	max_enqueued_footprint_bytes_(max_enqueued_footprint_bytes),
	target_installed_by_(std::move(target_installed_by)),
	raw_ds_config_(raw_ds_config) /* full copy */ {}

	} // namespace profiling
	} // namespace perfetto