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    SubjectRe: [PATCH 2/4] sched: cpufreq: Keep track of cpufreq utilization update flags
    On Wed, Dec 13, 2017 at 03:23:21PM +0530, Viresh Kumar wrote:
    > Currently the schedutil governor overwrites the sg_cpu->flags field on
    > every call to the utilization handler. It was pretty good as the initial
    > implementation of utilization handlers, there are several drawbacks
    > though.
    >
    > The biggest drawback is that the sg_cpu->flags field doesn't always
    > represent the correct type of tasks that are enqueued on a CPU's rq. For
    > example, if a fair task is enqueued while a RT or DL task is running, we
    > will overwrite the flags with value 0 and that may take the CPU to lower
    > OPPs unintentionally. There can be other corner cases as well which we
    > aren't aware of currently.
    >
    > This patch changes the current implementation to keep track of all the
    > task types that are currently enqueued to the CPUs rq. A new flag: CLEAR
    > is introduced and is set by the scheduling classes when their last task
    > is dequeued. When the CLEAR flag bit is set, the schedutil governor resets
    > all the other flag bits that are present in the flags parameter. For
    > now, the util update handlers return immediately if they were called to
    > clear the flag.

    Yeah, not happy about this either; we had code that did the right thing
    without this extra tracking I think.

    Also, we can look at the rq state if we want to, we don't need to
    duplicate that state.

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