From: Scott Wood <scottwood@freescale•com>
To: Anton Blanchard <anton@samba•org>
Cc: rric@kernel•org, oprofile-list@lists•sf.net, paulus@samba•org,
linuxppc-dev@lists•ozlabs.org
Subject: Re: [PATCH 2/2] powerpc: Add ppc64 hard lockup detector support
Date: Thu, 9 Apr 2015 18:48:01 -0500 [thread overview]
Message-ID: <1428623281.22867.558.camel@freescale.com> (raw)
In-Reply-To: <1428547976-24890-2-git-send-email-anton@samba.org>
On Thu, 2015-04-09 at 12:52 +1000, Anton Blanchard wrote:
> The hard lockup detector uses a PMU event as a periodic NMI to
> detect if we are stuck (where stuck means no timer interrupts have
> occurred).
>
> Ben's rework of the ppc64 soft disable code has made ppc64 PMU
> exceptions a partial NMI. They can get disabled if an external
> interrupt comes in, but otherwise PMU interrupts will fire in
> interrupt disabled regions.
>
> We disable the hard lockup detector by default for a few reasons:
>
> - It breaks userspace event based branches on POWER8.
> - It is likely to produce false positives on KVM guests.
What causes the false positives with KVM? I'm wondering if it makes
sense to enable this by default for book3e.
> - Since PMCs can only count to 2^31, counting cycles means we might
> take multiple PMU exceptions per second per hardware thread even
> if our hard lockup timeout is 10 seconds.
It'd be nice if this could be used with some event other than
PERF_COUNT_HW_CPU_CYCLES, such as something based on the timebase -- or
using the actual watchdog on book3e which would not consume a perf
counter and would be a full NMI as long as MSR[CE] is left on.
-Scott
next prev parent reply other threads:[~2015-04-09 23:48 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-09 2:52 [PATCH 1/2] oprofile: Disable oprofile NMI timer on ppc64 Anton Blanchard
2015-04-09 2:52 ` [PATCH 2/2] powerpc: Add ppc64 hard lockup detector support Anton Blanchard
2015-04-09 23:48 ` Scott Wood [this message]
2015-04-09 5:43 ` [PATCH 1/2] oprofile: Disable oprofile NMI timer on ppc64 Robert Richter
-- strict thread matches above, loose matches on Subject: below --
2015-01-21 3:46 [PATCH 1/2] oprofile: Add HAVE_OPROFILE_NMI_TIMER Anton Blanchard
2015-01-21 3:46 ` [PATCH 2/2] powerpc: Add ppc64 hard lockup detector support Anton Blanchard
2014-08-05 4:55 [PATCH 1/2] powerpc: Hard disable interrupts in xmon Anton Blanchard
2014-08-05 4:56 ` [PATCH 2/2] powerpc: Add ppc64 hard lockup detector support Anton Blanchard
2014-08-11 23:31 ` Anton Blanchard
2014-08-11 23:42 ` Paul E. McKenney
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