linux-kernel - Re: Using a new perf tool against an older kernel

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Message-ID: <4E041D2B.5020808@gmail.com>
Date:	Thu, 23 Jun 2011 23:14:19 -0600
From:	David Ahern <dsahern@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Arun Sharma <asharma@...com>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Using a new perf tool against an older kernel

On 06/23/2011 06:11 PM, Frederic Weisbecker wrote:
> On Thu, Jun 23, 2011 at 02:02:15PM -0600, David Ahern wrote:
>>
>>
>> On 06/23/2011 01:39 PM, Arun Sharma wrote:
>>> On 6/23/11 7:22 AM, David Ahern wrote:
>>>
>>>> I have not seen issues like this using newer perf userspace against
>>>> older kernels. For example, my laptop was running Fedora 14 (2.6.35) and
>>>> now Fedora 15 (2.6.38.8) and I typically use latest perf builds (e.g.,
>>>> testing patches).
>>>
>>> I narrowed it down to PERF_SAMPLE_RAW:
>>>
>>> perf record -ag -- sleep 1
>>>
>>> is fine, but:
>>>
>>> perf record -agR -- sleep 1
>>>
>>> fails for me most of the time. The reason I needed to use the -R in the
>>> first place is that "perf script" fails on older kernels with:
>>>
>>> Samples do not contain timestamps.
>>>
>>> With the newer perf, I don't get errors, but the timestamp field is
>>> invalid. So I need to use the -R flag to get valid timestamps +
>>> stacktraces out of "perf script".
>>
>> That should have been fixed.
>>
>> And -T on record gets the timestamps.
>>
>> David
> 
> Right, it would be nice to suggest that from perf script when timestamps
> are not recorded.

Timestamps are enabled by default, but that output option is removed if
the samples do not have timestamps. That message is generated if the
user requests timestamps (-f time) in the perf-script output and the
samples do not have timestamps, but Arun did not request that. Arun's
mileage with perf-3.0 definitely varies from what I've seen.

David
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