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From:   Chen Yu <yu.chen.surf@gmail.com>
Date:   Thu, 30 Nov 2023 14:43:00 +0800
Message-ID: <CADjb_WTFrPAgf5h1af4GuMFJ8UrDjzCPb_K+SZFo5s80xcniVA@mail.gmail.com>
Subject: Re: [PATCH v2 3/3] sched/fair: do not scribble cache-hot CPU in select_idle_cpu()
To:     Madadi Vineeth Reddy <vineethr@linux.ibm.com>
Cc:     Chen Yu <yu.c.chen@intel.com>, Tim Chen <tim.c.chen@intel.com>,
        Aaron Lu <aaron.lu@intel.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mel Gorman <mgorman@suse.de>,
        K Prateek Nayak <kprateek.nayak@amd.com>,
        "Gautham R . Shenoy" <gautham.shenoy@amd.com>,
        linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Ingo Molnar <mingo@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Juri Lelli <juri.lelli@redhat.com>
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Hi Madadi,

On Thu, Nov 30, 2023 at 1:26=E2=80=AFAM Madadi Vineeth Reddy
<vineethr@linux.ibm.com> wrote:
>
> Hi Chen Yu,
>
[snip...]

>
> As per my understanding, if the task which tagged a particular CPU as cac=
he hot has woken up before
> the cache_hot_timeout, we still don't allow that task to run on that part=
icular CPU. Is this correct?
>

Not exactly. When we reached select_idle_cpu(), we have already
checked if the wakee's previous CPU
is idle or not in select_idle_sibling(), if it is idle, we don't check
the cache-hot tag and return the wakee's
previous CPU directly in select_idle_sibling().

thanks,
Chenyu

> If correct, then why don't we let the task to select the CPU if it's the =
one that tagged it?
>
> Thanks and Regards
> Madadi Vineeth Reddy