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[71.255.246.27]) by smtp.gmail.com with ESMTPSA id m21sm9043990qka.117.2020.02.03.04.07.58 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 03 Feb 2020 04:07:59 -0800 (PST) Subject: Re: [Patch v9 7/8] sched/fair: Enable tuning of decay period To: Randy Dunlap , mingo@redhat.com, peterz@infradead.org, ionela.voinescu@arm.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rui.zhang@intel.com, qperret@google.com, daniel.lezcano@linaro.org, viresh.kumar@linaro.org, rostedt@goodmis.org, will@kernel.org, catalin.marinas@arm.com, sudeep.holla@arm.com, juri.lelli@redhat.com, corbet@lwn.net References: <1580250967-4386-1-git-send-email-thara.gopinath@linaro.org> <1580250967-4386-8-git-send-email-thara.gopinath@linaro.org> <4eb10687-1a62-cee3-7285-3f50cc023071@infradead.org> Cc: linux-kernel@vger.kernel.org, amit.kachhap@gmail.com, javi.merino@kernel.org, amit.kucheria@verdurent.com From: Thara Gopinath Message-ID: <5E380D1D.7020500@linaro.org> Date: Mon, 3 Feb 2020 07:07:57 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <4eb10687-1a62-cee3-7285-3f50cc023071@infradead.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/28/2020 06:56 PM, Randy Dunlap wrote: > Hi, > > On 1/28/20 2:36 PM, Thara Gopinath wrote: >> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt >> index e35b28e..be4147b 100644 >> --- a/Documentation/admin-guide/kernel-parameters.txt >> +++ b/Documentation/admin-guide/kernel-parameters.txt >> @@ -4376,6 +4376,11 @@ >> incurs a small amount of overhead in the scheduler >> but is useful for debugging and performance tuning. >> >> + sched_thermal_decay_shift= >> + [KNL, SMP] Set decay shift for thermal pressure signal. >> + Format: integer between 0 and 10 >> + Default is 0. >> + > > That tells an admin [or any reader] almost nothing about this kernel parameter > or what it does. And nothing about what unit the value is in. > Does the value 0 disable this feature? Thanks for the review. 0 does not disable "thermal pressure" feature. 0 means the default decay period for averaging PELT signals (which is usually 32 but configurable) will also be applied for thermal pressure signal. A shift will shift the default decay period. You are right. It needs more explanation here. I will fix it and send v10. > >> skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate >> xtime_lock contention on larger systems, and/or RCU lock >> contention on all systems with CONFIG_MAXSMP set. > > > thanks. > -- Warm Regards Thara