linux-kernel - Re: [PATCH 1/2 v2] tracing/core: use appropriate waiting on trace

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Date:	Wed, 18 Feb 2009 01:40:47 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH 1/2 v2] tracing/core: use appropriate waiting on
	trace_pipe


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Wed, Feb 11, 2009 at 02:25:00AM +0100, Frederic Weisbecker wrote:
> > Impact: api and pipe waiting change
> > 
> > Currently, the waiting used in tracing_read_pipe() is done through a
> > 100 msecs schedule_timeout() loop which periodically check if there
> > are traces on the buffer.
> > 
> > This can cause small latencies for programs which are reading the incoming
> > events.
> > 
> > This patch makes the reader waiting for the trace_wait waitqueue except
> > for few tracers such as the sched and functions tracers which might be
> > already hold the runqueue lock while waking up the reader.
> > 
> > This is performed through a new callback wait_pipe() on struct tracer.
> > If none is implemented on a specific tracer, the default waiting for
> > trace_wait queue is attached.
> > 
> > Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> > ---
> >  kernel/trace/trace.c                 |   62 ++++++++++++++++++++++-----------
> >  kernel/trace/trace.h                 |   25 ++++++++++++--
> >  kernel/trace/trace_functions.c       |    1 +
> >  kernel/trace/trace_functions_graph.c |    1 +
> >  kernel/trace/trace_sched_switch.c    |    1 +
> >  kernel/trace/trace_sched_wakeup.c    |    1 +
> >  6 files changed, 67 insertions(+), 24 deletions(-)
> 
> 
> Steven, Ingo, do you agree this one?
> 
> Thanks.

yeah - this version is much cleaner. I've applied it to 
tip:tracing/ftrace, thanks Frederic!

	Ingo
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