linux-kernel - Re: [PATCH 1/3] perf: add context field to perf

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Date:	Wed, 29 Jun 2011 19:25:58 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>, a.p.zijlstra@...llo.nl,
	acme@...stprotocols.net, Will Deacon <will.deacon@....com>,
	Jason Wessel <jason.wessel@...driver.com>
Subject: Re: [PATCH 1/3] perf: add context field to perf_event

On 06/29/2011 07:08 PM, Frederic Weisbecker wrote:
> On Wed, Jun 29, 2011 at 06:42:35PM +0300, Avi Kivity wrote:
> >  The perf_event overflow handler does not receive any caller-derived
> >  argument, so many callers need to resort to looking up the perf_event
> >  in their local data structure.  This is ugly and doesn't scale if a
> >  single callback services many perf_events.
> >
> >  Fix by adding a context parameter to perf_event_create_kernel_counter()
> >  (and derived hardware breakpoints APIs) and storing it in the perf_event.
> >  The field can be accessed from the callback as event->overflow_handler_context.
> >  All callers are updated.
> >
> >  Signed-off-by: Avi Kivity<avi@...hat.com>
>
> I believe it can micro-optimize ptrace through register_user_hw_breakpoint() because
> we could store the index of the breakpoint that way, instead of iterating through 4 slots.
>

Right, I noticed that while writing the patch.

> Perhaps it can help in arm too, adding Will in Cc.
>
> But for register_wide_hw_breakpoint, I'm not sure. kgdb is the main user, may be Jason
> could find some use of it.

I think an API should not require its users to iterate in their 
callbacks, even if it doesn't affect current users for some reason.

-- 
error compiling committee.c: too many arguments to function

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