linux-kernel - Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

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Message-ID: <49A81D05.4040807@redhat.com>
Date:	Fri, 27 Feb 2009 12:04:05 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	systemtap-ml <systemtap@...rces.redhat.com>
Subject: Re: [PATCH] tracing/ftrace: add missing wake-up on some callsites

Steven Rostedt wrote:
> On Mon, 23 Feb 2009, Ingo Molnar wrote:
> 
>> * Steven Rostedt <rostedt@...dmis.org> wrote:
>>
>>>> Which would send a delayed work to wake up?
>>> No, I was thinking that trace_delay_wake_up() would be called 
>>> by these dangerous call sites. Then a per_cpu flag could be 
>>> set. We could have a trace point in the scheduler code that is 
>>> outside holding a runqueue lock, and this trace point would 
>>> call a trace function that will clear the per cpu flag, and 
>>> then call trace_wake_up().
>> No, that's very roundabout and ugly. If we putting a tracepoint 
>> there we might as well put real scheduler code there that looks 
>> for such a flag. But i'm not convinced we need a flag ...
> 
> Just a suggestion. I was trying to keep the tracer from being an overhead. 
> But what else would you suggest? Just having the scheduler call 
> trace_wakeup?

Actually, Systemtap(LTTng too?) also has same problem. Currently,
we're using a periodical timer to wake the reader process up.
I assume if we can put a tracepoint at the beginning of schedule(),
we can share it.

Thank you,


> 
> -- Steve
> 
> --
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-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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