Merge "docs: Address comments on concurrent-tracing-sessions.md" into main
diff --git a/docs/concepts/concurrent-tracing-sessions.md b/docs/concepts/concurrent-tracing-sessions.md
index a9ab94a..63f6dd4 100644
--- a/docs/concepts/concurrent-tracing-sessions.md
+++ b/docs/concepts/concurrent-tracing-sessions.md
@@ -6,23 +6,24 @@
However there are a few caveats to bear in mind with concurrent tracing sessions:
1. [Some data sources do not support concurrent sessions](#some-data-sources-do-not-support-concurrent-sessions)
2. [Some settings are per session while others are per producer](#some-settings-are-per-session-while-others-are-per-producer)
-3. Due to the [way atrace works works](#atrace) if session requests *any* atrace category or app it receives *all* atrace events enabled on the device
+3. Due to the [way atrace works works](#atrace) if a session requests *any* atrace category or app it receives *all* atrace events enabled on the device
4. [Various limits](#various-limits) apply
## Some data sources do not support concurrent sessions
-While most data sources implemented with the Perfetto SDK as most of the data sources provided by the Perfetto team support concurrent tracing sessions others do not. This can be due to:
+Whilst most data sources implemented with the Perfetto SDK as well as most data sources provided by the Perfetto team, do support concurrent tracing sessions some do not.
+This can be due to:
-- HW or driver constraints
+- Hardware or driver constraints
- Difficulty of implementing the config muxing
- Perfetto SDK: users may [opt-out of multiple session support](https://cs.android.com/android/platform/superproject/main/+/main:external/perfetto/include/perfetto/tracing/data_source.h;l=266;drc=f988c792c18f93841b14ffa71019fdedf7ab2f03)
### Known to work
-- `traced_probes` datasources
+- `traced_probes` data sources ([linux.ftrace](/docs/reference/trace-config-proto.autogen#FtraceConfig), [linux.process_stats](/docs/reference/trace-config-proto.autogen#ProcessStatsConfig), [linux.sys_stats](/docs/reference/trace-config-proto.autogen#SysStatsConfig), [linux.system_info](https://perfetto.dev/docs/reference/trace-config-proto.autogen#SystemInfoConfig), etc)
### Known to work with caveats
- `heapprofd` supports multiple sessions but each process can only be in one session.
-- `traced_perf` in general supports but the kernel has a limit on counters so may reject a config.
+- `traced_perf` in general supports multiple sessions but the kernel has a limit on counters so may reject a config.
### Known not to work
- `traced metatracing`
@@ -32,7 +33,7 @@
Most buffer sizes and timings specified in the config are per session.
For example the buffer [sizes](https://cs.android.com/android/platform/superproject/main/+/main:external/perfetto/protos/perfetto/config/trace_config.proto;l=32?q=f:perfetto%20f:trace_config&ss=android%2Fplatform%2Fsuperproject%2Fmain).
-However some parameters configure per-producer settings. For example the [size and layout](https://cs.android.com/android/platform/superproject/main/+/main:external/perfetto/protos/perfetto/config/trace_config.proto;l=182;drc=488df1649781de42b72e981c5e79ad922508d1e5) of the shmem buffer between the producer and traced.
+However some parameters configure per-producer settings: for example the [size and layout](https://cs.android.com/android/platform/superproject/main/+/main:external/perfetto/protos/perfetto/config/trace_config.proto;l=182;drc=488df1649781de42b72e981c5e79ad922508d1e5) of the shmem buffer between the producer and traced.
While that is general data source setting the same can apply to data source specific settings.
For example the ftrace [kernel buffer size and drain period](https://cs.android.com/android/platform/superproject/main/+/main:external/perfetto/protos/perfetto/config/ftrace/ftrace_config.proto;l=32;drc=6a3d3540e68f3d5949b5d86ca736bfd7f811deff) are settings that have to be shared between all users of `traced_probes`.
@@ -49,7 +50,7 @@
Atrace (both prior to Perfetto and via Perfetto) works as follows:
- Configuration:
- Users choose zero or more 'categories' from a hardcoded list
- - Users choose zero of package names including globs
+ - Users choose zero or more package names including globs
- This sets:
- Some kernel ftrace events
- A [system property bitmask](https://cs.android.com/android/platform/superproject/main/+/main:frameworks/native/cmds/atrace/atrace.cpp;l=306;drc=c8af4d3407f3d6be46fafdfc044ace55944fb4b7) (for the atrace categories)
@@ -57,7 +58,7 @@
- When the Java or C++ tracing APIs are called we examine the system props.
- If the relevant category or package is enabled we write the event to `trace_marker`
-As mentioned each category may enable a number of kernel ftrace events.
+As mentioned, each category may enable a number of kernel ftrace events.
For example the 'sched' atrace category enables the `sched/sched_switch` ftrace event.
Kernel ftrace events do not suffer from the current session issues so will not be described further.
@@ -66,10 +67,10 @@
- However since:
- the atrace system properties are global
- we cannot tell which event comes from which category/package
-- every session that requests *any* atrace event gets *all* enabled atrace events.
+Every session that requests *any* atrace event gets *all* enabled atrace events.
## Various limits
-- Perfetto SDK: Max 8 datasource intances per datasource type per producer
+- Perfetto SDK: Max 8 datasource instances per datasource type per producer
- `traced`: Limit of [15 concurrent sessions](https://cs.android.com/android/platform/superproject/main/+/main:external/perfetto/src/tracing/service/tracing_service_impl.cc;l=114?q=kMaxConcurrentTracingSessions%20)
- `traced`: Limit of [5 (10 for statsd) concurrent sessions per UID](https://cs.android.com/android/platform/superproject/main/+/main:external/perfetto/src/tracing/service/tracing_service_impl.cc;l=115;drc=17d5806d458e214bdb829deeeb08b098c2b5254d)
