RE: [PATCH 3/4] cpuidle: teo: Consider hits and misses metrics of disabled states

From: "Doug Smythies" <dsmythies@telus.net>
To: "'Rafael J. Wysocki'" <rjw@rjwysocki.net>
Cc: "'Linux PM'" <linux-pm@vger.kernel.org>,
	"'LKML'" <linux-kernel@vger.kernel.org>,
	"'Srinivas Pandruvada'" <srinivas.pandruvada@linux.intel.com>,
	"'Peter Zijlstra'" <peterz@infradead.org>,
	"'Daniel Lezcano'" <daniel.lezcano@linaro.org>
Subject: RE: [PATCH 3/4] cpuidle: teo: Consider hits and misses metrics of disabled states
Date: Tue, 5 Nov 2019 11:50:38 -0800	[thread overview]
Message-ID: <001601d59412$4db298d0$e917ca70$@net> (raw)
In-Reply-To: <2237950.TTgtiEjdez@kreacher>

On 2019.10.10 14:36 Rafael J. Wysocki wrote:

> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> The TEO governor uses idle duration "bins" defined in accordance with
> the CPU idle states table provided by the driver, so that each "bin"
> covers the idle duration range between the target residency of the
> idle state corresponding to it and the target residency of the closest
> deeper idle state.  The governor collects statistics for each bin
> regardless of whether or not the idle state corresponding to it is
> currently enabled.
>
> In particular, the "hits" and "misses" metrics measure the likelihood
> of a situation in which both the time till the next timer (sleep
> length) and the idle duration measured after wakeup fall into the
> given bin.  Namely, if the "hits" value is greater than the "misses"
> one, that situation is more likely than the one in which the sleep
> length falls into the given bin, but the idle duration measured after
> wakeup falls into a bin corresponding to one of the shallower idle
> states.
>
> If the idle state corresponding to the given bin is disabled, it
> cannot be selected and if it turns out to be the one that should be
> selected, a shallower idle state needs to be used instead of it.
> Nevertheless, the metrics collected for the bin corresponding to it
> are still valid and need to be taken into account as though that
> state had not been disabled.
>
> For this reason, make teo_select() always use the "hits" and "misses"
> values of the idle duration range that the sleep length falls into
> even if the specific idle state corresponding to it is disabled and
> if the "hits" values is greater than the "misses" one, select the
> closest enabled shallower idle state in that case.
> 
> Fixes: b26bf6ab716f ("cpuidle: New timer events oriented governor for tickless systems")
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Great thanks.

Acked-by: Doug Smythies <dsmythies@telus.net>