linux-kernel - Re: Preemptionirqsoff latency issue

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Date:	Fri, 9 Jan 2015 11:25:05 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Vaibhav Shinde <v.bhav.shinde@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, tj@...nel.org,
	Davidlohr Bueso <dave@...olabs.net>
Subject: Re: Preemptionirqsoff latency issue

On Fri, 9 Jan 2015 20:19:51 +0530
Vaibhav Shinde <v.bhav.shinde@...il.com> wrote:

> Hi Peter,
> 
> Thanks for you reply.
> 
> I am interested in scheduling latency, and using ftrace I see for my
> application suffering from it, that's why I am digging in preemption/irq
> disable time which might cause the latency.
> 
> My app runs on cpu0, while other cpus looks idle; as per my understanding
> from your comment owner of the mutex is on the cpu other than cpu0, and
> which is causing wait spin on cpu0.
> Can this be the reason why latency is caused ?
> If so, then I think I need to take care of the mutex lock which is called
> from my code.
> 

If you download and install the latest trace-cmd, you may be able to
get more information with its new command "profile".

 # trace-cmd profile -o  file  workload

Then look at the output in file.

To limit the running to tracing only the workload:

 # trace-cmd profile -o file -F -c workload

You'll need to use the latest that's in my repo. Use the master branch,
as it has all the above features.

 git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/trace-cmd.git

-- Steve
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