From: khilman@kernel•org (Kevin Hilman)
To: linux-arm-kernel@lists•infradead.org
Subject: [RFC PATCH 2/2] arm64: kernel: perf: add pmu CPU PM notifier
Date: Wed, 11 Mar 2015 09:02:17 -0700 [thread overview]
Message-ID: <7hh9try12u.fsf@deeprootsystems.com> (raw)
In-Reply-To: <1426008682-5680-2-git-send-email-lorenzo.pieralisi@arm.com> (Lorenzo Pieralisi's message of "Tue, 10 Mar 2015 17:31:22 +0000")
Lorenzo Pieralisi <lorenzo.pieralisi@arm•com> writes:
> When a CPU is being profiled through PMU events and it enters suspend
> or idle states, the PMU registers content can be lost, which means that
> counters that were relied upon on power down entry are reset on power
> up to values that are incosistent with the profile session.
>
> This patch adds a CPU PM notifier to arm64 perf code, that detects
> on entry if events are being monitored, and if so, it returns
> failure to the CPU PM notification chain, causing the suspend
> thread or the idle thread to abort power down, therefore preventing
> registers content loss.
>
> By triggering CPU PM notification failure this patch prevents
> suspending a system if the suspend thread is being profiled and
> it also prevents entering idle deep states on cores that have profile
> events in use, somehow limiting power management capabilities when
> there are active perf sessions.
I guess that's one choice. Couldn't you also stop the PMU and
save/restore it's context in the notifiers? so that you wouldn't affect
PM capabilities?
That would imply that you lose the ability to profile after a certain
point in suspend/idle, but maybe that's a better trade off than having
profiling disable certain PM features?
Kevin
next prev parent reply other threads:[~2015-03-11 16:02 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-10 17:31 [RFC PATCH 1/2] arm64: kernel: perf: add cpu hotplug notifier Lorenzo Pieralisi
2015-03-10 17:31 ` [RFC PATCH 2/2] arm64: kernel: perf: add pmu CPU PM notifier Lorenzo Pieralisi
2015-03-11 16:02 ` Kevin Hilman [this message]
2015-03-12 10:27 ` Lorenzo Pieralisi
2015-03-12 13:18 ` Ashwin Chaugule
2015-03-13 17:40 ` Lorenzo Pieralisi
2015-03-13 23:31 ` Kevin Hilman
2015-03-17 17:24 ` Will Deacon
2015-03-30 17:45 ` Lorenzo Pieralisi
2015-03-31 16:35 ` Kevin Hilman
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