Message-ID: <2037831.3FXZ8RTMPh@vostro.rjw.lan>
Date:	Wed, 26 Feb 2014 01:46:25 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Tuukka Tikkanen <tuukka.tikkanen@...aro.org>
Cc:	linux-pm@...r.kernel.org, daniel.lezcano@...aro.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/7] Cpuidle: Minor fixes

On Monday, February 24, 2014 08:29:30 AM Tuukka Tikkanen wrote:
> This set of patches makes some minor changes to menu governor and the poll
> idle state.
> 
> Patch 1 is simply a rename of a variable to make the name better represent
> the contained information.
> 
> Patch 2 fixes calculating actual residency in cases where the entered state
> is different from the state decided by the menu governor.
> 
> Patch 3 makes sure the menu governor timer coefficients are not updated
> with values that might cause a coefficient to reach a value greater than
> unity.
> 
> Patch 4 fixes calculation actual residency in cases where the entered state
> does not support measuring residency. In such cases the residency time
> is taken from time remaining until next timer expiry. The timer is expected
> to go off at the start of exit latency, not after it. Therefore the exit
> latency must not be substracted from the assumed value.
> 
> Patch 5 moves the performance multiplier based comparison out of the state
> selection loop by changing it into a latency requirement. This allows
> using a generic state selection function accepting only (duration, latency)
> tuple as input. The change is possible by noting that performance multiplier
> is used only to check for a minimum predicted idle duration to exit latency
> ratio. As predicted idle duration is a constant for the loop, the maximum
> allowed latency can be calculated outside of the loop.
> 
> Patch 6 prevents using negative values from tick_nohz_get_sleep_length()
> in the menu governor. If unchecked, the negative values are used as huge
> unsigned values. Negative values occur fairly often (e.g. on x86_64 I've
> seen this happen several times per minute) on a busy system, allowing
> the deepest state to win the selection while the shallowest should be picked.
> 
> Patch 7 adds CPUIDLE_FLAG_TIME_VALID to poll_idle. I do not know of any
> platfrom where cpu_relax() would break ktime_get() and in fact poll_idle
> uses ktime_get itself.
> (Note: poll_idle updates dev->last_residency for some reason. Does it ever
> get called without going through cpuidle_enter_state, which will overwrite
> the value? Even if some state redirects to this state, the call will
> eventually return to the framework. The redundant time measurement could
> be removed, unless there is some obscure way of getting called on some
> platform that I am unable to figure out.)
> 
> Tuukka Tikkanen (7):
>   Cpuidle: rename expected_us to next_timer_us in menu governor
>   Cpuidle: Use actual state latency in menu governor
>   Cpuidle: Ensure menu coefficients stay within domain
>   Cpuidle: Do not substract exit latency from assumed sleep length
>   Cpuidle: Move perf multiplier calculation out of the selection loop
>   Cpuidle: Deal with timer expiring in the past
>   Cpuidle: poll state can measure residency
> 
>  drivers/cpuidle/driver.c         |    2 +-
>  drivers/cpuidle/governors/menu.c |   85 ++++++++++++++++++++++++--------------
>  2 files changed, 54 insertions(+), 33 deletions(-)

I'm queuing this series up for 3.15.

It looks like at least some of these patches should go into 3.14 and -stable,
but for that I'd need some references like links to bug reports or documented
reproducibility (on what hardware, what it takes to reproduce etc.).

Thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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