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Subject: Re: [RFC PATCH v4] sched/fair: select idle cpu from idle cpumask for
 task wakeup
To:     Valentin Schneider <valentin.schneider@arm.com>
Cc:     mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, mgorman@techsingularity.net,
        qais.yousef@arm.com, dietmar.eggemann@arm.com, rostedt@goodmis.org,
        bsegall@google.com, tim.c.chen@linux.intel.com,
        linux-kernel@vger.kernel.org, Aubrey Li <aubrey.li@intel.com>,
        Mel Gorman <mgorman@suse.de>, Jiang Biao <benbjiang@gmail.com>
References: <20201116200428.47359-1-aubrey.li@linux.intel.com>
 <jhjlfeyx41f.mognet@arm.com>
From:   "Li, Aubrey" <aubrey.li@linux.intel.com>
Message-ID: <bf7b6dd3-7922-2a4e-8df5-735b24c2dfc7@linux.intel.com>
Date:   Thu, 19 Nov 2020 09:13:09 +0800
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On 2020/11/18 20:06, Valentin Schneider wrote:
> 
> On 16/11/20 20:04, Aubrey Li wrote:
>> From: Aubrey Li <aubrey.li@intel.com>
>>
>> Add idle cpumask to track idle cpus in sched domain. When a CPU
>> enters idle, if the idle driver indicates to stop tick, this CPU
>> is set in the idle cpumask to be a wakeup target. And if the CPU
>> is not in idle, the CPU is cleared in idle cpumask during scheduler
>> tick to ratelimit idle cpumask update.
>>
>> When a task wakes up to select an idle cpu, scanning idle cpumask
>> has low cost than scanning all the cpus in last level cache domain,
>> especially when the system is heavily loaded.
>>
>> Benchmarks were tested on a x86 4 socket system with 24 cores per
>> socket and 2 hyperthreads per core, total 192 CPUs. Hackbench and
>> schbench have no notable change, uperf has:
>>
>> uperf throughput: netperf workload, tcp_nodelay, r/w size = 90
>>
>>   threads       baseline-avg    %std    patch-avg       %std
>>   96            1               0.83    1.23            3.27
>>   144           1               1.03    1.67            2.67
>>   192           1               0.69    1.81            3.59
>>   240           1               2.84    1.51            2.67
>>
>> Cc: Mel Gorman <mgorman@suse.de>
>> Cc: Vincent Guittot <vincent.guittot@linaro.org>
>> Cc: Qais Yousef <qais.yousef@arm.com>
>> Cc: Valentin Schneider <valentin.schneider@arm.com>
>> Cc: Jiang Biao <benbjiang@gmail.com>
>> Cc: Tim Chen <tim.c.chen@linux.intel.com>
>> Signed-off-by: Aubrey Li <aubrey.li@linux.intel.com>
> 
> That's missing a v3 -> v4 change summary
> 

okay, I'll add in the next version soon.

Thanks,
-Aubrey