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SubjectRe: [PATCH V3 0/2] sched/fair: Fallback to sched-idle CPU in absence of idle CPUs
On Wed, 26 Jun 2019 at 13:07, Viresh Kumar <> wrote:
> Hi,
> We try to find an idle CPU to run the next task, but in case we don't
> find an idle CPU it is better to pick a CPU which will run the task the
> soonest, for performance reason.
> A CPU which isn't idle but has only SCHED_IDLE activity queued on it
> should be a good target based on this criteria as any normal fair task
> will most likely preempt the currently running SCHED_IDLE task
> immediately. In fact, choosing a SCHED_IDLE CPU over a fully idle one
> shall give better results as it should be able to run the task sooner
> than an idle CPU (which requires to be woken up from an idle state).
> This patchset updates both fast and slow paths with this optimization.
> Testing is done with the help of rt-app currently and here are the
> details:
> - Tested on Octacore Hikey platform (all CPUs change frequency
> together).
> - rt-app json [1] creates few tasks and we monitor the scheduling
> latency for them by looking at "wu_lat" field (usec).
> - The histograms are created using
> textogram -a 0 -z 1000 -n 10
> - the stats are accumulated using:

Hi Viresh,

Thanks for the great work! Could you give the whole commad-line for us testing?


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