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

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Message-ID: <20110624001145.GE8058@somewhere.redhat.com>
Date:	Fri, 24 Jun 2011 02:11:48 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	David Ahern <dsahern@...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 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.
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