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

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Message-ID: <CABPqkBRUzp-gBANhiMerHanN7yaTnJbxHNEjz_mw+XRYT8ZHUw@mail.gmail.com>
Date:	Mon, 27 Feb 2012 18:52:25 +0100
From:	Stephane Eranian <eranian@...gle.com>
To:	David Ahern <dsahern@...il.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 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...



> David
>
>>
>>  void event_attr_init(struct perf_event_attr *attr)
>>  {
>> --
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>
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