linux-kernel - Re: [PATCH 3/4] perf_events: Support a lock

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Message-ID: <4E78D2A2.6010106@linux.intel.com>
Date:	Tue, 20 Sep 2011 10:51:30 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Andi Kleen <andi@...stfloor.org>, acme@...stprotocols.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] perf_events: Support a lock_parent event flag


> This all just sucks horridly. So this name tells us we need inherited
> counters so that whenever we encounter a lock it will be accounted in
> the parent process, or whatever -- which doesn't make any sense.

Thanks for the kind words. So what name do you suggest?

account_in_caller_of_lock ?

i_write_a_novel_in_every_variable_name?

> Furthermore, the sole reason you want this is because you don't want
> callchains, supposedly because they're too expensive, but then you don't
> say that.

perf top doesn't support callchains. And yes it's a lot cheaper too, but 
that wasn't
the main motivation. perf top is just useless to diagnose any lock problems
currently.

I say that in the changelog for the user space.

> How about you provide means of limiting the callchain depth, and then
> frob the in_lock_function() and unwind 1 crap in userspace?

Is that equivalent? The normal call chains don't work without frame 
pointers.
profile_pc does.

-Andi

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