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From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Paul Mackerras <paulus@samba.org>,
	David Miller <davem@davemloft.net>
Subject: Re: [PATCH 2/2] perf: Use hot regs with software sched switch/migrate events
Date: Mon, 29 Mar 2010 10:49:59 +0200	[thread overview]
Message-ID: <1269852599.12097.159.camel@laptop> (raw)
In-Reply-To: <1269753066-17246-3-git-send-regression-fweisbec@gmail.com>

On Sun, 2010-03-28 at 07:11 +0200, Frederic Weisbecker wrote:
> Scheduler's task migration events don't work because they always
> pass NULL regs perf_sw_event(). The event hence gets filtered
> in perf_swevent_add().
> 
> Scheduler's context switches events use task_pt_regs() to get
> the context when the event occured which is a wrong thing to
> do as this won't give us the place in the kernel where we went
> to sleep but the place where we left userspace. The result is
> even more wrong if we switch from a kernel thread.
> 
> Use the hot regs snapshot for both events as they belong to the
> non-interrupt/exception based events family. Unlike page faults
> or so that provide the regs matching the exact origin of the event,
> we need to save the current context.
> 
> This makes the task migration event working and fix the context
> switch callchains and origin ip.


But after this its no longer possible to profile userspace on context
switches is it?


  reply	other threads:[~2010-03-29  9:11 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-03-28  5:11 [GIT PULL] perf fixes Frederic Weisbecker
2010-03-28  5:11 ` [PATCH 1/2] perf: Correctly align perf event tracing buffer Frederic Weisbecker
2010-03-29  8:51   ` Peter Zijlstra
2010-03-29 17:16     ` Frederic Weisbecker
2010-03-29 17:20       ` Peter Zijlstra
2010-03-29 17:51         ` Frederic Weisbecker
2010-03-28  5:11 ` [PATCH 2/2] perf: Use hot regs with software sched switch/migrate events Frederic Weisbecker
2010-03-29  8:49   ` Peter Zijlstra [this message]
2010-03-29 17:47     ` Frederic Weisbecker
2010-03-29 18:05       ` Peter Zijlstra
2010-03-29 22:43         ` Frederic Weisbecker
2010-03-29 22:53           ` Frederic Weisbecker
2010-03-30 18:54           ` Peter Zijlstra
2010-03-30 19:14             ` Frederic Weisbecker
2010-03-29  3:33 ` [GIT PULL] perf fixes Ingo Molnar

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