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    SubjectRe: [PATCH v2] schedutil: Allow cpufreq requests to be made even when kthread kicked
    On 21/05/18 10:29, Rafael J. Wysocki wrote:
    > On Mon, May 21, 2018 at 7:14 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote:
    > > On 18-05-18, 11:55, Joel Fernandes (Google.) wrote:
    > >> From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
    > >>
    > >> Currently there is a chance of a schedutil cpufreq update request to be
    > >> dropped if there is a pending update request. This pending request can
    > >> be delayed if there is a scheduling delay of the irq_work and the wake
    > >> up of the schedutil governor kthread.
    > >>
    > >> A very bad scenario is when a schedutil request was already just made,
    > >> such as to reduce the CPU frequency, then a newer request to increase
    > >> CPU frequency (even sched deadline urgent frequency increase requests)
    > >> can be dropped, even though the rate limits suggest that its Ok to
    > >> process a request. This is because of the way the work_in_progress flag
    > >> is used.
    > >>
    > >> This patch improves the situation by allowing new requests to happen
    > >> even though the old one is still being processed. Note that in this
    > >> approach, if an irq_work was already issued, we just update next_freq
    > >> and don't bother to queue another request so there's no extra work being
    > >> done to make this happen.
    > >
    > > Now that this isn't an RFC anymore, you shouldn't have added below
    > > paragraph here. It could go to the comments section though.
    > >
    > >> I had brought up this issue at the OSPM conference and Claudio had a
    > >> discussion RFC with an alternate approach [1]. I prefer the approach as
    > >> done in the patch below since it doesn't need any new flags and doesn't
    > >> cause any other extra overhead.
    > >>
    > >> [1] https://patchwork.kernel.org/patch/10384261/
    > >>
    > >> LGTMed-by: Viresh Kumar <viresh.kumar@linaro.org>
    > >> LGTMed-by: Juri Lelli <juri.lelli@redhat.com>
    > >
    > > Looks like a Tag you just invented ? :)
    >
    > Yeah.
    >
    > The LGTM from Juri can be converned into an ACK silently IMO. That

    Sure! :)

    Thanks,

    - Juri

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