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

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Date:	Tue, 28 Apr 2009 19:49:36 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Oleg Nesterov <oleg@...hat.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 Tue, Apr 28, 2009 at 06:43:42PM +0200, Oleg Nesterov wrote:
> 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).



Hmm. Yes, basing this tracing against the workqueue as a unit basis
using per_cpu buffers seems rather more natural.


 
> > 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.
> 



Yeah, it means we should separate cleanup and destroy events.


> 
> 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.
> 


The changes you suggest seem to me logical and could simplify this
tracer.
So I will apply Zhaolei patches and then start addressing
your comments :-)


> > 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 ;)


Thanks!


> Oleg.
> 

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