linux-kernel - Re: [PATCH -tip 3/3] Add get

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Date:	Tue, 17 Nov 2009 10:26:30 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Roland McGrath <roland@...hat.com>,
	lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>
Subject: Re: [PATCH -tip 3/3] Add get_signal tracepoint

Ingo Molnar wrote:
> 
> * Masami Hiramatsu <mhiramat@...hat.com> wrote:
> 
>>>  - signal IPI/wakeup events
>>
>> All signals might be used for IPI, isn't it? :-)
> 
> I mean, to analyze the various dynamic delivery details of how a signal 
> send affects a target task:
> 
>  1) which task/PID was selected to be woken
> 
>  2) if the task got woken (from sleep) due to the signal sending
> 
>  3) if it was already woken, whether it needed an IPI via kick_process()

Hmm, as far as I can see, some of these events can be caught by
sched layer too.
- trace_signal_send() will record target task.
- wake_up_state() just calls try_to_wake_up(), and trace_sched_wakeup()
  will be called from it.
- kick_process() might better have its own tracepoint.

And also, I think signal_wake_up() might not be a good tracepoint for
signal event, since there is no signr. Moreover some signal_wake_up()
caller(e.g. recalc_sigpending*) silently wake up processes :-(.

> What proportion of signals were wakeups and what proportion hit an 
> already running task is a relevant question to ask when analyzing the 
> performance characteristics of signals.

Hmm, does it really require wakeup events in signal layer?
I think that we can analyze the characteristics by combination
of signal events and sched events.

Thank you,
-- 
Masami Hiramatsu

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

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

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