linux-kernel - Re: [PATCH] powerpc: perf: power_pmu_start restores incorrect values, breaking frequency events

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Date:	Sun, 19 Feb 2012 12:13:18 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Anton Blanchard <anton@...ba.org>, peterz@...radead.org,
	mingo@...e.hu, gleb@...hat.com, wcohen@...hat.com,
	vince@...ter.net, asharma@...com, andi@...stfloor.org,
	emunson@...bm.net, imunsie@....ibm.com, benh@...nel.crashing.org,
	sukadev@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc: perf: power_pmu_start restores incorrect values,
 breaking frequency events

Glad to see you fixed the PPC problem.

On Thu, Feb 16, 2012 at 5:57 AM, Paul Mackerras <paulus@...ba.org> wrote:
> On Thu, Feb 16, 2012 at 03:48:22PM +1100, Anton Blanchard wrote:
>>
>> perf on POWER stopped working after commit e050e3f0a71b (perf: Fix
>> broken interrupt rate throttling). That patch exposed a bug in
>> the POWER perf_events code.
>>
>> Since the PMCs count upwards and take an exception when the top bit
>> is set, we want to write 0x80000000 - left in power_pmu_start. We were
>> instead programming in left which effectively disables the counter
>> until we eventually hit 0x80000000. This could take seconds or longer.
>>
>> With the patch applied I get the expected number of samples:
>>
>> # taskset -c 0 yes > /dev/null &
>> # perf record -C 0 -a sleep 10
>> # perf report -D | grep SAMPLE | tail -1
>>           SAMPLE events:       9948
>>
>> Signed-off-by: Anton Blanchard <anton@...ba.org>
>
> Acked-by: Paul Mackerras <paulus@...ba.org>
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