src/traced/probes/ftrace/ftrace_metadata.h

/*
 * Copyright (C) 2017 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.
 */

#ifndef SRC_TRACED_PROBES_FTRACE_FTRACE_METADATA_H_
#define SRC_TRACED_PROBES_FTRACE_FTRACE_METADATA_H_

#include <stdint.h>
#include <sys/stat.h>
#include <unistd.h>

#include <bitset>

#include "perfetto/base/flat_set.h"
#include "perfetto/base/logging.h"
#include "perfetto/ext/traced/data_source_types.h"

namespace perfetto {

using BlockDeviceID = decltype(stat::st_dev);
using Inode = decltype(stat::st_ino);

// Container for tracking miscellaneous information while parsing ftrace events,
// scoped to an individual data source. Cleared periodically, after the metadata
// is processed by the data sources interested in it, see
// |OnFtraceDataWrittenIntoDataSourceBuffers|.
struct FtraceMetadata {
  struct KernelAddr {
    KernelAddr(uint64_t _addr, uint32_t _index) : addr(_addr), index(_index) {}
    uint64_t addr = 0;
    uint32_t index = 0;

    // We never keep more than one KernelAddr entry per address in the set. This
    // is really just a workaround for the lack of a FlatMap.
    // The |index| is written only after the entry is added to the set, to have
    // a monotonic value that reflects the insertion order.
    friend bool operator<(const KernelAddr& lhs, const KernelAddr& rhs) {
      return lhs.addr < rhs.addr;
    }
    friend bool operator==(const KernelAddr& lhs, const KernelAddr& rhs) {
      return lhs.addr == rhs.addr;
    }
  };

  FtraceMetadata() {
    // A sched_switch is 64 bytes, a page is 4096 bytes and we expect
    // 2 pid's per sched_switch. 4096/64*2=128. Give it a 2x margin.
    pids.reserve(256);

    // We expect to see only a small number of task rename events.
    rename_pids.reserve(32);

    kernel_addrs.reserve(256);
  }

  void AddDevice(BlockDeviceID device_id) {
    last_seen_device_id = device_id;
#if PERFETTO_DCHECK_IS_ON()
    seen_device_id = true;
#endif
  }

  void AddInode(Inode inode_number) {
#if PERFETTO_DCHECK_IS_ON()
    PERFETTO_DCHECK(seen_device_id);
#endif
    static int32_t cached_pid = 0;
    if (!cached_pid)
      cached_pid = getpid();

    PERFETTO_DCHECK(last_seen_common_pid);
    PERFETTO_DCHECK(cached_pid == getpid());
    // Ignore own scanning activity.
    if (cached_pid != last_seen_common_pid) {
      inode_and_device.insert(
          std::make_pair(inode_number, last_seen_device_id));
    }
  }

  void AddRenamePid(int32_t pid) { rename_pids.insert(pid); }

  void AddPid(int32_t pid) {
    const size_t pid_bit = static_cast<size_t>(pid);
    if (PERFETTO_LIKELY(pid_bit < pids_cache.size())) {
      if (pids_cache.test(pid_bit))
        return;
      pids_cache.set(pid_bit);
    }
    pids.insert(pid);
  }

  void AddCommonPid(int32_t pid) {
    last_seen_common_pid = pid;
    AddPid(pid);
  }

  // Returns the index of the symbol (a monotonic counter, which is set when
  // the symbol is inserted the first time).
  uint32_t AddSymbolAddr(uint64_t addr) {
    auto it_and_inserted = kernel_addrs.insert(KernelAddr(addr, 0));
    // Deliberately prefer a branch here to always computing and passing
    // size + 1 to the above.
    if (it_and_inserted.second) {
      const auto index = static_cast<uint32_t>(kernel_addrs.size());
      it_and_inserted.first->index = index;
    }
    return it_and_inserted.first->index;
  }

  void Clear() {
    inode_and_device.clear();
    rename_pids.clear();
    pids.clear();
    pids_cache.reset();
    kernel_addrs.clear();
    fds.clear();
    last_kernel_addr_index_written = 0;
    FinishEvent();
  }

  void FinishEvent() {
    last_seen_device_id = 0;
    last_seen_common_pid = 0;
#if PERFETTO_DCHECK_IS_ON()
    seen_device_id = false;
#endif
  }

  BlockDeviceID last_seen_device_id = 0;
#if PERFETTO_DCHECK_IS_ON()
  bool seen_device_id = false;
#endif
  int32_t last_seen_common_pid = 0;
  uint32_t last_kernel_addr_index_written = 0;

  base::FlatSet<InodeBlockPair> inode_and_device;
  base::FlatSet<int32_t> rename_pids;
  base::FlatSet<int32_t> pids;
  base::FlatSet<KernelAddr> kernel_addrs;
  base::FlatSet<std::pair<pid_t, uint64_t>> fds;

  // This bitmap is a cache for |pids|. It speculates on the fact that on most
  // Android kernels, PID_MAX=32768. It saves ~1-2% cpu time on high load
  // scenarios, as AddPid() is a very hot path.
  std::bitset<32768> pids_cache;
};

}  // namespace perfetto

#endif  // SRC_TRACED_PROBES_FTRACE_FTRACE_METADATA_H_