linux-kernel - Re: [PATCH] workqueue: Add basic tracepoints to track workqueue execution

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Date:	Sun, 22 Aug 2010 05:21:57 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Arjan van de Ven <arjan@...radead.org>, Ingo Molnar <mingo@...e.hu>
Cc:	tj@...nel.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, rostedt@...dmis.org
Subject: Re: [PATCH] workqueue: Add basic tracepoints to track workqueue
	execution

On Sat, Aug 21, 2010 at 01:14:02PM -0700, Arjan van de Ven wrote:
> 
> From: Arjan van de Ven <arjan@...ux.intel.com>
> Date: Sat, 21 Aug 2010 13:07:26 -0700
> Subject: [PATCH] workqueue: Add basic tracepoints to track workqueue execution
> 
> With the introduction of the new unified work queue thread pools,
> we lost one feature: It's no longer possible to know which worker
> is causing the CPU to wake out of idle. The result is that PowerTOP
> now reports a lot of "kworker/a:b" instead of more readable results.
> 
> This patch adds a pair of tracepoints to the new workqueue code,
> similar in style to the timer/hrtimer tracepoints.
> 
> With this pair of tracepoints, the next PowerTOP can correctly
> report which work item caused the wakeup (and how long it took):
> 
> Interrupt (43)            i915      time   3.51ms    wakeups 141
> Work      ieee80211_iface_work      time   0.81ms    wakeups  29
> Work              do_dbs_timer      time   0.55ms    wakeups  24
> Process                   Xorg      time  21.36ms    wakeups   4
> Timer    sched_rt_period_timer      time   0.01ms    wakeups   1
> 
> Signed-off-by: Arjan van de Ven <arjan@...ux.intel.com>



Acked-by: Frederic Weisbecker <fweisbec@...il.com>


If that broke a userspace tool, should that perhaps go to .36 ?
I know it's a big patch, but in fact it's more a semi-revert of
the workqueue tracepoints removal.

It's my bad in fact: I suggested Tejun not to bother with workqueue
tracepoints yet and to drop the previous ones for now. The previous ones were
placed to observe problems specific to the purely serialized design they
had. I thought cmwq would need other tracepoints.

In fact I thought no tools were using these tracepoints. Bad assumption...

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