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From: Ingo Molnar <mingo@kernel.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org,
	eranian@google.com, Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH 1/2] Fix perf LBR filtering
Date: Wed, 1 May 2013 13:55:49 +0200	[thread overview]
Message-ID: <20130501115549.GA19811@gmail.com> (raw)
In-Reply-To: <20130501115125.GA19497@gmail.com>


* Ingo Molnar <mingo@kernel.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

      reply	other threads:[~2013-05-01 11:56 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-04-24 23:04 [PATCH 1/2] Fix perf LBR filtering Andi Kleen
2013-04-24 23:04 ` [PATCH 2/2] perf, x86: Don't allow unusual PEBS raw flags Andi Kleen
2013-04-29 22:16   ` Stephane Eranian
2013-04-29 22:34     ` Andi Kleen
2013-04-29 23:05       ` Stephane Eranian
2013-05-02  7:37   ` Peter Zijlstra
2013-05-06 17:44     ` Stephane Eranian
2013-05-06 18:52       ` Peter Zijlstra
2013-05-06 22:43         ` Stephane Eranian
2013-05-07  6:48           ` Ingo Molnar
2013-05-07  8:48             ` Peter Zijlstra
2013-05-07 11:04               ` Ingo Molnar
2013-05-07  8:43           ` Peter Zijlstra
2013-04-24 23:20 ` [PATCH 1/2] Fix perf LBR filtering Ben Hutchings
2013-04-24 23:24 ` Greg KH
2013-04-25 16:25 ` Peter Zijlstra
2013-04-25 16:41   ` Andi Kleen
2013-04-25 16:48     ` Peter Zijlstra
2013-04-25 17:00       ` Andi Kleen
2013-04-25 17:18         ` Peter Zijlstra
2013-04-25 17:42           ` Andi Kleen
2013-04-26  7:56             ` Peter Zijlstra
2013-04-26 19:46               ` Andi Kleen
2013-05-01 11:51                 ` Ingo Molnar
2013-05-01 11:55                   ` Ingo Molnar [this message]

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