linux-kernel - Re: [PATCH] perf tools: fix guest mode monitoring on AMD

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Message-ID: <4F4BC4A4.10006@gmail.com>
Date:	Mon, 27 Feb 2012 11:00:04 -0700
From:	David Ahern <dsahern@...il.com>
To:	Stephane Eranian <eranian@...gle.com>
CC:	linux-kernel@...r.kernel.org, acme@...hat.com,
	robert.richter@....com, peterz@...radead.org, mingo@...e.hu,
	joro@...tes.org, gleb@...hat.com, joerg.roedel@....com
Subject: Re: [PATCH] perf tools: fix guest mode monitoring on AMD

On 2/27/12 10:52 AM, Stephane Eranian wrote:
> On Mon, Feb 27, 2012 at 6:47 PM, David Ahern<dsahern@...il.com>  wrote:
>> On 2/27/12 10:33 AM, Stephane Eranian wrote:
>>>
>>> Commit:
>>>
>>> 1aed267 perf kvm: Do guest-only counting by default
>>>
>>> introduced a bug on AMD systems whereby simple commands:
>>>
>>> $ perf stat ls
>>> Performance counter stats for 'ls':
>>>                   0 cycles                    #    0.000 GHz
>>>         0.003704596 seconds time elapsed
>>>
>>> would not count anything anymore. Same results for perf record.
>>>
>>> I tracked it down to guest mode exclusion being enabled
>>> by default leading to attr->exclude_guest = 1. When
>>> not operating under any sort of virtualization, this
>>> causes the PMU not to count anything.
>>>
>>> The fix disables guest exclusion by default.
>>>
>>> Signed-off-by: Stephane Eranian<eranian@...gle.com>
>>> ---
>>>
>>> diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c
>>> index 8109a90..c1017b3 100644
>>> --- a/tools/perf/util/util.c
>>> +++ b/tools/perf/util/util.c
>>> @@ -6,7 +6,7 @@
>>>    * XXX We need to find a better place for these things...
>>>    */
>>>   bool perf_host  = true;
>>> -bool perf_guest = false;
>>> +bool perf_guest = true;
>>
>>
>> This was recently reverted to false by
>> c4a7dca92bbb9881a5d678720f1d0c2153499749
>>
>> See: https://lkml.org/lkml/2012/2/8/234
>>
> Yeah, but that causes simple commands such as "perf stat -e cycles ls"
> to return 0 count.
>
> So either you get a segfault or you get zero count. There is something
> else going on here...

agreed. Did you try reverting exclude_guest by default?

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