Sukadev Bhattiprolu [suka...@linux.vnet.ibm.com] wrote:
|
| >From 21e9d1775f0c6f37a39e5d682ff74693fa9a4004 Mon Sep 17 00:00:00 2001
| From: Sukadev Bhattiprolu <suka...@linux.vnet.ibm.com>
| Date: Tue, 7 Aug 2012 17:53:24 -0700
| Subject: [PATCH] Use pmc_overflow to detect rolled back events.
|
| For certain speculative events on Power7, 'perf stat' reports far higher
| event count than 'perf record' for the same event.
|
| As described in following commit, a performance monitor exception is raised
| even when the the performance events are rolled back.
|
| commit 0837e3242c73566fc1c0196b4ec61779c25ffc93
| Author: Anton Blanchard <an...@samba.org>
| Date: Wed Mar 9 14:38:42 2011 +1100
|
| perf_event_interrupt() records an event only when an overflow occurs. But
| this check for overflow is a simple 'if (val < 0)'.
|
| Because the events are rolled back, this check for overflow fails and the
| event is not recorded. perf_event_interrupt() later uses pmc_overflow() to
| detect the overflow and resets the counters and the events are lost
completely.
|
| To properly detect the overflow of rolled back events, use pmc_overflow()
| even when recording events.
Ben,
Sorry for the noise, but please revert this patch (following commit):
commit 813312110bede27bffd082c25cd31730bd567beb
Author: Sukadev Bhattiprolu <suka...@linux.vnet.ibm.com>
Date: Tue Aug 7 15:07:19 2012 +0000
While it does fix the problem described above and works for the limit-pmc
events, it seems to break on Power7 for other events and when the sample
period is low.
I am still investigating the problem and will follow up with a separate
mail.
Sukadev
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