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Fri, 31 Jan 2020 12:33:28 -0800 (PST) Received: from kozik-lap ([194.230.155.229]) by smtp.googlemail.com with ESMTPSA id g9sm651960ejd.66.2020.01.31.12.33.26 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 31 Jan 2020 12:33:27 -0800 (PST) Date: Fri, 31 Jan 2020 21:33:24 +0100 From: Krzysztof Kozlowski To: Lukasz Luba Subject: Re: [PATCH 1/3] ARM: exynos_defconfig: Enable SCHED_MC Message-ID: <20200131203324.GA27510@kozik-lap> References: <20200127215453.15144-1-lukasz.luba@arm.com> <20200127215453.15144-2-lukasz.luba@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200131_123330_421748_306760C7 X-CRM114-Status: GOOD ( 23.73 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, devicetree@vger.kernel.org, "linux-samsung-soc@vger.kernel.org" , linux-pm@vger.kernel.org, =?utf-8?Q?Bart=C5=82omiej_=C5=BBo=C5=82nierkiewicz?= , "linux-kernel@vger.kernel.org" , robh+dt@kernel.org, Chanwoo Choi , kyungmin.park@samsung.com, kgene@kernel.org, myungjoo.ham@samsung.com, dietmar.eggemann@arm.com, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Jan 31, 2020 at 03:59:30PM +0000, Lukasz Luba wrote: > Hi Krzysztof, > > Thank you for your review, please see my comments below. > > On 1/31/20 12:47 PM, Krzysztof Kozlowski wrote: > > On Mon, 27 Jan 2020 at 22:55, wrote: > > > > > > From: Lukasz Luba > > > > > > Since the 'capacities-dmips-mhz' are present in the CPU nodes, make use of > > > this knowledge in smarter decisions during scheduling. > > > > > > The values in 'capacities-dmips-mhz' are normilized, this means that i.e. > > > when CPU0's capacities-dmips-mhz=100 and CPU1's 'capacities-dmips-mhz'=50, > > > cpu0 is twice fast as CPU1, at the same frequency. The proper hirarchy > > > in sched_domain topology could exploit the SoC architecture advantages > > > like big.LITTLE. > > > > I do not quite get how this is related to rationale behind changing defconfig... > > It is not strictly about EAS, it is useful in general for big.LITTLE > platform with clusters. > > > > > > Enabling the SCHED_MC will create two levels in > > > sched_domain hierarchy, which might be observed in: > > > > This is looks more convincing... but still what is the need? To work with EAS? > > It is not only for EAS, but in general for the scheduler (load balance, > task's wake-up path, etc). The scheduler algorithms iterate CPUs in the > sched groups. To make better decisions, the information about MC domain > is needed. More about the scheduler domains and i.e. load_balance() > you can find here: > > https://www.kernel.org/doc/html/latest/scheduler/sched-domains.html Ahhh, I see, it's independent of later patches. Somehow I had impression it is a prerequisite... > > > > > > grep . /proc/sys/kernel/sched_domain/cpu*/domain*/{name,flags} > > > /proc/sys/kernel/sched_domain/cpu0/domain0/name:MC > > > /proc/sys/kernel/sched_domain/cpu0/domain1/name:DIE > > > ... > > > /proc/sys/kernel/sched_domain/cpu0/domain0/flags:575 > > > /proc/sys/kernel/sched_domain/cpu0/domain1/flags:4223 > > > > Not related to defconfig change and not visible after this commit. > > Without this patch there is only one domain: 'domain0' -> 'DIE' > cat /proc/sys/kernel/sched_domain/cpu0/domain0/name > DIE > > When you apply this patch you will get two: 'domain0, 'domain1' > grep . /proc/sys/kernel/sched_domain/cpu0/domain?/name > > /proc/sys/kernel/sched_domain/cpu0/domain0/name:MC > /proc/sys/kernel/sched_domain/cpu0/domain1/name:DIE > > I can remove it this information, but it is the most important > to spot this difference out. > > This is also the main reason I haven't merge the patch 1 + 3. Indeed. I thought that these will pop up at the end of the patchset, my bad. I do not see big benefits of adding these outputs as proofs of working SCHED_MC because they are kind of obvious. It is not a measurement but report of current system state. However they don't harm neither, so I am fine with it. However please us in commit msg also the name of turned on option, next or instead of SCHED_MC. The options might be sometimes cryptic or too vague and the name actually easily expresses what you want enable. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel