linux-kernel - Re: [PATCH v3 1/1] ftrace, workqueuetrace: Make workqueuetracepoints use TRACE

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Date:	Tue, 21 Apr 2009 00:25:14 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Zhaolei <zhaolei@...fujitsu.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tom Zanussi <tzanussi@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] ftrace, workqueuetrace: Make
	workqueuetracepoints use TRACE_EVENT macro

On 04/20, Ingo Molnar wrote:
>
> Andrew, Oleg: if you plan to make unhappy noises about this level of
> instrumentation in the workqueue code, please do it sooner rather
> than later, as there's quite some effort injected into this already.
> A tentative non-NAK now (patches are still being sorted out) and an
> Ack on the final topic tree from you (once we send it and if it's
> good) and general happiness would be the ideal outcome :)

Imho, this info is useful, and the changes are fine.

But I didn't study kernel/trace/trace_workqueue.c yet... Sorry, I was
going to do this, but I didn't.

At first glance, with or without these new changes some parts of
trace_workqueue.c looks suspicious.

For example, I don't understand cpu_workqueue_stats->pid. Why it is
needed? Why can't we just record wq_thread itself? And if we copy
wq_thread->comm to cpu_workqueue_stats, we don't even need get/put
task_struct, afaics.

probe_workqueue_destruction() does cpumask_first(cwq->cpus_allowed),
this doesn't look right. When workqueue_cpu_callback() calls
cleanup_workqueue_thread(), wq_thread is no longer affine to CPU it
was created on. This means probe_workqueue_destruction() can't always
find the correct cpu_workqueue_stats in workqueue_cpu_stat(cpu), no?

Oleg.

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