linux-kernel - Re: perf_counters: page fault trace record

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Message-ID: <18995.28357.164575.925080@cargo.ozlabs.ibm.com>
Date:	Sat, 13 Jun 2009 19:17:57 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Corey Ashford <cjashfor@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: perf_counters: page fault trace record

Corey Ashford writes:

> Paul Mackerras wrote:
> > Can't you do what you need just using a page fault software counter
> > with sample_type = PERF_SAMPLE_IP | PERF_SAMPLE_ADDR and
> > sample_period = 1?
> 
> I thought about that, but I was under the (incorrect?) impression that 
> on Power, the PERF_SAMPLE_ADDR would be set by the value of the SDAR 
> register, which wouldn't be correct for the case of a page fault.

No, the PERF_SAMPLE_ADDR value only comes from SDAR for a hardware
counter overflow event.  For the page-fault software counter the
PERF_SAMPLE_ADDR value will always be the faulting address.

Paul.
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