From: Peter Zijlstra <peterz@infradead.org>
To: Matt Fleming <matt@console-pimps.org>
Cc: Zhang Rui <rui.zhang@intel.com>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
Frederic Weisbecker <fweisbec@gmail.com>,
Robert Richter <robert.richter@amd.com>,
Lin Ming <ming.m.lin@intel.com>,
Paul Mackerras <paulus@samba.org>,
Arnaldo Carvalho de Melo <acme@redhat.com>,
Don Zickus <dzickus@redhat.com>,
Cyrill Gorcunov <gorcunov@gmail.com>, Len Brown <lenb@kernel.org>,
Matthew Garrett <mjg59@srcf.ucam.org>
Subject: Re: [RFC][PATCH 3/5] perf: Add hrtimer code for PMI-less hardware counters
Date: Mon, 30 Aug 2010 14:55:02 +0200 [thread overview]
Message-ID: <1283172902.1820.897.camel@laptop> (raw)
In-Reply-To: <38d993baf1328403d9a1c4a2f012c4aa0e19feab.1283123521.git.matt@console-pimps.org>
On Mon, 2010-08-30 at 13:13 +0100, Matt Fleming wrote:
> Currently, it's impossible to periodically sample hardware counters that
> lack performance monitoring interrupt (PMI) support. In order to sample
> these counters we can create an event group which is backed by a
> hrtimer, thereby simulating a PMI.
>
> When the hrtimer goes off we sample the values in the hardware
> counters. Because we obviously can't rely on the hrtimer going off at
> exactly the sample period (say, every 1000 cache misses) the values need
> to be weighted by the variable period since the last hrtimer went
> off. This is so that we can compensate for the variability in hrtimer
> period.
>
> If perf record tries to create a sampling counter and the hardware
> doesn't support it then we'll fall back to creating an event group with
> a hrtimer.
Why is this changing kernel code?
You can create those groups in userspace..
next prev parent reply other threads:[~2010-08-30 12:55 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-30 12:13 [RFC][PATCH 0/5] hrtimer group events Matt Fleming
2010-08-30 12:13 ` [RFC][PATCH 1/5] perf: Check if we should exclude idle thread in perf_exclude_event() Matt Fleming
2010-08-31 14:54 ` Frederic Weisbecker
2010-08-31 15:20 ` Matt Fleming
2010-08-31 15:21 ` Frederic Weisbecker
2010-08-30 12:13 ` [RFC][PATCH 2/5] perf: Turn the group counter values into delta values Matt Fleming
2010-08-30 12:54 ` Peter Zijlstra
2010-08-30 13:21 ` Matt Fleming
2010-08-30 12:13 ` [RFC][PATCH 3/5] perf: Add hrtimer code for PMI-less hardware counters Matt Fleming
2010-08-30 12:55 ` Peter Zijlstra [this message]
2010-08-30 13:27 ` Matt Fleming
2010-08-30 14:12 ` Peter Zijlstra
2010-08-30 19:35 ` Matt Fleming
2010-08-30 12:13 ` [RFC][PATCH 4/5] sh: Add support for sampling counters Matt Fleming
2010-08-30 12:13 ` [RFC][PATCH 5/5] perf: Add support for PERF_SAMPLE_READ samples Matt Fleming
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