linux-kernel - Re: [PATCH 18/21] cpuidle: don't call poll_idle

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Date:	Thu, 26 Sep 2013 10:28:27 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Patch Tracking <patches@...aro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 18/21] cpuidle: don't call poll_idle_init() for every
 cpu

On 09/26/2013 08:09 AM, Viresh Kumar wrote:
> On 26 September 2013 03:52, Daniel Lezcano <daniel.lezcano@...aro.org> wrote:
>> On 09/22/2013 03:21 AM, Viresh Kumar wrote:
>>> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
>
> This deserved a log, sorry for missing that :(
>
>> The optimization sounds good but IMHO if we can move this state out of
>> the cpuidle common framework that would be nicer.
>>
>> The poll_idle is only applicable for x86 (acpi_driver and intel_idle),
>> hence I suggest we move this state to these drivers, that will cleanup
>> the framework code and will remove index shift macro
>> CPUIDLE_DRIVER_STATE_START which IMHO is weid and prone-to-error.
>
> Lets see what X86 folks have to say about it and then we can do it..
> Btw, wouldn't that add some code duplication in those two drivers?

Yes, certainly and that will impact also the menu select governor function:

  ...

         /*
          * We want to default to C1 (hlt), not to busy polling
          * unless the timer is happening really really soon.
          */
         if (data->expected_us > 5 &&
             !drv->states[CPUIDLE_DRIVER_STATE_START].disabled &&
                 dev->states_usage[CPUIDLE_DRIVER_STATE_START].disable == 0)
                 data->last_state_idx = CPUIDLE_DRIVER_STATE_START;

         /*
          * Find the idle state with the lowest power while satisfying
          * our constraints.
          */
         for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
                 struct cpuidle_state *s = &drv->states[i];
                 struct cpuidle_state_usage *su = &dev->states_usage[i];

                 if (s->disabled || su->disable)
                         continue;
                 if (s->target_residency > data->predicted_us)
                         continue;
                 if (s->exit_latency > latency_req)
                         continue;
                 if (s->exit_latency * multiplier > data->predicted_us)
                         continue;

                 data->last_state_idx = i;
                 data->exit_us = s->exit_latency;
         }

....

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