Re: [PATCH V2 1/5] sched: idle: cpuidle: Check the latency req before idle
From: Daniel Lezcano
Date: Wed Nov 05 2014 - 16:41:16 EST
On 11/05/2014 10:57 PM, Rafael J. Wysocki wrote:
On Thursday, October 23, 2014 11:01:17 AM Daniel Lezcano wrote:
When the pmqos latency requirement is set to zero that means "poll in all the
cases".
That is correctly implemented on x86 but not on the other archs.
As how is written the code, if the latency request is zero, the governor will
return zero, so corresponding, for x86, to the poll function, but for the
others arch the default idle function. For example, on ARM this is wait-for-
interrupt with a latency of '1', so violating the constraint.
In order to fix that, do the latency requirement check *before* calling the
cpuidle framework in order to jump to the poll function without entering
cpuidle. That has several benefits:
1. It clarifies and unifies the code
2. It fixes x86 vs other archs behavior
3. Factors out the call to the same function
4. Prevent to enter the cpuidle framework with its expensive cost in
calculation
As the latency_req is needed in all the cases, change the select API to take
the latency_req as parameter in case it is not equal to zero.
As a positive side effect, it introduces the latency constraint specified
externally, so one more step to the cpuidle/scheduler integration.
I'm expecting to see a new version of this patchset relatively soon.
Are you planning to send one?
I would like to find an agreement with Preeti. But, yes, I am on it.
-- Daniel
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