linux-kernel - Re: [PATCH][RFC] Measuring term of acquiring spinlock

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Message-ID: <20091113105126.GC5243@nowhere>
Date:	Fri, 13 Nov 2009 11:51:27 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Hitoshi Mitake <mitake@....info.waseda.ac.jp>
Cc:	mingo@...e.hu, a.p.zijlstra@...llo.nl, tglx@...utronix.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RFC] Measuring term of acquiring spinlock

On Fri, Nov 13, 2009 at 01:21:25PM +0900, Hitoshi Mitake wrote:
> > Might make sense to put it into 'perf lock' kind of tool. I think 
> > Frederic had such plans.
> 
> If you want a tester for 'perf lock', please call me, Frederic :)


Thanks :)
I haven't started it yet, because of some other things I need to finish.

Would you be interested in starting it?

The lock tracepoints are:

- lock_acquire: the lock is requested but not yet "acquired"
- lock_release
- lock_contended: we can't get the lock yet because someone already
  holds it.
- lock_acquired: we got the lock


So, the point would be to develop a state machine that is
able to give us statistics on a per lock granularity
basis:


- the total/average/maximum time a lock is contended,
  waited before being acquired (probably
  lock_acquired time - lock_acquire time)

- the ratio of contention versus immediate availability
  => Sequence acquire - acquired means immediate
     availability. If we have a contended event inside
     it means it had to wait because of the contention.

- the total/average/maximum time a lock is held.
  It would be very nice to also add an option to see the
  callsites sorted from max to min, if possible with a per
  boundary granularity: the couple (lock callsite, unlock callsite),
  still on a per lock basis.

- any idea you could have...


Such a tool would be very useful to profile the kernel locking.

It would be nice to use design close to what perf sched does:
having an lock event structure that provides callbacks for each
lock events so that we can easily plug various plugin inside.

It's just a suggestion in case you are interested and have time
for that. Otherwise I'll do it later.

Hm?

Thanks,
	Frederic.

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