linux-kernel - Re: [PATCH] ftracetest: Do not use usleep

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Date:	Tue, 31 Mar 2015 09:48:55 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Shuah Khan <shuahkh@....samsung.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Dave Jones <davej@...emonkey.org.uk>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: Re: [PATCH] ftracetest: Do not use usleep

Hi Steve,

On Mon, Mar 30, 2015 at 05:15:11PM -0400, Steven Rostedt wrote:
> On Thu, 26 Mar 2015 09:32:23 +0900
> Namhyung Kim <namhyung@...nel.org> wrote:
> 
> > The usleep is only provided on distros from Redhat so running ftracetest
> > on other distro resulted in failures due to the missing usleep.
> > 
> > The reason of using [u]sleep in the test was to generate (scheduler)
> > events. But as we use 'cat trace | grep | wc -l' to read the events,
> > the command themselves already generate some events before reading the
> > trace file so no need to call [u]sleep explicitly.
> 
> Note, opening "trace" via cat stops tracing. There is a possible race
> where the cat will not produce events. My worry is that if the shell
> implements its own "cat" command, it may not fork, and open the trace
> file. Which would not have any events in it, and opening it will
> disable the rest of the command from having events.

I understand your point.  But this is not just cat, it needs grep and
wc also.  So I think there should be scheduler event(s).

> 
> What about using:
> 
>  ping localhost -c 1
> 
> ?

I'm okay with ping though but worried if some tiny system might lack
the ping command..

Thanks,
Namhyung
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