linux-kernel - Re: [PATCH 1/2] Fix perf LBR filtering

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Message-ID: <20130501115549.GA19811@gmail.com>
Date:	Wed, 1 May 2013 13:55:49 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	eranian@...gle.com, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/2] Fix perf LBR filtering


* Ingo Molnar <mingo@...nel.org> wrote:

> > I don't think you want to spend that many cycles in the NMI
> > handler for a dubious feature.  Ok in theory you could
> > add something with binary search, but that would be quite
> > a bit of effort and it would be probably challenging 
> > to do that all NMI safe.
> 
> If anyone using LBR sees that overhead it can be improved. You or others 
> who care can improve it.

Also, improving the performance of is_module_text() shouldn't be too hard: 
an RCU rbtree should be enough.

It's NMI-safe: when the rb-tree is in the middle of a rotation we'll 
simply not find the address and 'revert' to the worst case non-filtering 
your patch does all the time, but in the likely case it does find it and 
works as expected.

Thanks,

	Ingo
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