Re: [PATCH v3 linux-trace 1/8] tracing: attach eBPF programs to tracepoints and syscalls

From: Peter Zijlstra
Date: Wed Feb 11 2015 - 04:45:58 EST

On Tue, Feb 10, 2015 at 04:22:50PM -0800, Alexei Starovoitov wrote:
> well, ->prio and ->pid are already printed by sched tracepoints
> and their meaning depends on scheduler. So users taking that
> into account.

Right, so trace_events were/are root only, and root 'should' be in the
root pid namespace, and therefore pid magically works.

And I'm not sure, but I don't think the 'nested' root available from
containers should have access to ftrace, so that should not be an issue.

Perf tries real hard to present PERF_SAMPLE_PID data in the pid
namespace of the task that created the event.

As to prio; yes this is a prime example of suck, I would love to change
that but cannot :-(. The only solace I have is that everybody who is
relying on it is broken.

There is a very good reason I'm against adding more tracepoints to the
scheduler, its a nightmare.

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