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

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Message-ID: <20150211094541.GO23123@twins.programming.kicks-ass.net>
Date:	Wed, 11 Feb 2015 10:45:41 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexei Starovoitov <ast@...mgrid.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v3 linux-trace 1/8] tracing: attach eBPF programs to
 tracepoints and syscalls

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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