linux-kernel - Re: perf support user-space hw

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Date:	Thu, 28 Jun 2012 12:12:53 +0800
From:	Jovi Zhang <bookjovi@...il.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel@...r.kernel.org
Subject: Re: perf support user-space hw_breakpoint?

Hi,

On Thu, Jun 28, 2012 at 10:20 AM, Namhyung Kim <namhyung@...nel.org> wrote:
> On Thu, 28 Jun 2012 09:02:02 +0800, Jovi Zhang wrote:
>> On Mon, Jun 25, 2012 at 4:26 PM, Namhyung Kim <namhyung@...nel.org> wrote:
>>> BTW, when I perf record on a hwbp, it failed with ENOSPC.
>>> I guess it's because each per-task-per-cpu event tried to
>>> create an event so it'd get more than supported by h/w.
>>> The strace told me that the fifth call to perf_event_open
>>> failed on my 6-core machine.
>>>
>> I have same result as you in my linux box.
>> This should be a bug cause by commit d1cb9f(perf target: Add uses_mmap field)
>>
>> Namhyung, How about below patch?
>>
>
> NAK. This uses_mmap field is needed to setup per-task-per-cpu events for
> perf record (mostly). Without it, perf suffered from severe scalability
> issues. Maybe we can change it not to create per-task-per-cpu events iff
> for hwbp events only, but I'm not sure it's the right thing.
>
> Thanks,
> Namhyung
>
perf tool create cpumaps and threadmaps for evlist, not for evsel, this means
we cannot easily create a dummy cpumaps for hwbp event even when
evlist include hwbp type evsel.

Any ideas?

.jovi
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