linux-kernel - Re: [PATCH] perf_events: fix bug in hw_perf

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Date:	Mon, 01 Feb 2010 17:45:31 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	davem@...emloft.net, fweisbec@...il.com, robert.richter@....com,
	perfmon2-devel@...ts.sf.net, eranian@...il.com,
	Arjan van de Ven <arjan@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] perf_events: fix bug in hw_perf_enable()

On Mon, 2010-02-01 at 17:14 +0100, Stephane Eranian wrote:

> Using perfmon on Core 2 on a 10s noploop:
> 
> pfmon -eunhalted_reference_cycles,unhalted_core_cycles,cpu_clk_unhalted:bus
>  noploop 10
> noploop for 10 seconds
> 23869090125 UNHALTED_REFERENCE_CYCLES
> 23849336873 UNHALTED_CORE_CYCLES
>  2652122099 CPU_CLK_UNHALTED:BUS 

Weird, I used:

 while :; do :; done &
 while :; do :; done &
 while :; do :; done &
 while :; do :; done &
 perf stat -a -e r013c -e r013c sleep 4
 killall bash

Which gives:

 Performance counter stats for 'sleep 4':

 244235699509090  raw 0x13c
 244235695558036  raw 0x13c

    4.005485333  seconds time elapsed

And verified it used fixed counter 2 and general purpose counter 0 using
sysrq-p.

[523417.108402] CPU#0:   gen-PMC0 ctrl:  000000000053013c
[523417.108403] CPU#0:   gen-PMC0 count: 000000ff80019948
[523417.108405] CPU#0:   gen-PMC0 left:  000000007fffffff
[523417.108407] CPU#0:   gen-PMC1 ctrl:  0000000000000000
[523417.108409] CPU#0:   gen-PMC1 count: 0000000000000000
[523417.108411] CPU#0:   gen-PMC1 left:  000000007fffb8a8
[523417.108412] CPU#0: fixed-PMC0 count: 0000000000000000
[523417.108414] CPU#0: fixed-PMC1 count: 0000000000000000
[523417.108416] CPU#0: fixed-PMC2 count: 0000010db1db2117

Using -linus, since that doesn't have any of the recent constraint
patches in that would avoid us from using fixed-PMC2.

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