linux-kernel - Re: [PATCH 0/4] workqueue_tracepoint: Add worklet tracepoints for worklet lifecycle tracing

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Date:	Tue, 28 Apr 2009 18:43:42 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, zhaolei@...fujitsu.com,
	kosaki.motohiro@...fujitsu.com, rostedt@...dmis.org,
	tzanussi@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] workqueue_tracepoint: Add worklet tracepoints for
	worklet lifecycle tracing

On 04/28, Frederic Weisbecker wrote:
>
> On Mon, Apr 27, 2009 at 05:02:41PM +0200, Oleg Nesterov wrote:
> >
> > I must admit, I don't really understand why trace_workqueue.c uses
> > cwq->thread as a "primary key". I have the feeling we can simplify
> > this code if we pass "struct workqueue_struct *" instead, but I am
> > not sure.
>
> Indeed, I wanted to use it as the identifier first. The problem
> is that this structure is privately defined inside kernel/workqueue.c

Perhaps we have to export some bits or add some simple helpers to
workqueue.c. But I am not sure trace/trace_workqueue.c actually needs
any additional info. Again, we can use "struct workqueue_struct *" as
a "void *", and probe_workqueue_creation() can use alloc_percpu() to
record the events per-cpu. (_Perhaps_, we can also add some fields
to workqueue_struct or cpu_workqueue_struct under #ifdef and eliminate
the list search code in trace_workqueue.c).

> But actually it's not really a 1:1 matching in CONFIG_HOTPLUG_CPU
> case, because the thread can destroyed and the cpu_workqueue assigned
> with a new one later.

Indeed, I also thought about this. This is subjective, but perhaps it
is better to keep the history. If not, we can clear it on CPU_DEAD.

But let me repeat, I am not very sure these changes are really good,
and I didn't try to really think about them. Even _if_ I am right
we can do this later.

> I'm currently gathering Zhaolei patches and I will push them all in
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing.git
>  tracing/workqueue

Thanks! Will try to look when I have the chance. Not that I think
I can really help though ;)

Oleg.

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