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[77.129.94.205]) by smtp.googlemail.com with ESMTPSA id b16sm7143988wrq.41.2019.03.22.06.26.07 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 22 Mar 2019 06:26:08 -0700 (PDT) Subject: Re: [PATCH 1/2] cpuidle : auto-promotion for cpuidle states To: "Rafael J. Wysocki" , Abhishek Goel References: <20190322072942.8038-1-huntbag@linux.vnet.ibm.com> <20190322072942.8038-2-huntbag@linux.vnet.ibm.com> From: Daniel Lezcano Message-ID: Date: Fri, 22 Mar 2019 14:26:07 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Rafael J. Wysocki" , linuxppc-dev , Linux Kernel Mailing List , Linux PM Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 22/03/2019 10:45, Rafael J. Wysocki wrote: > On Fri, Mar 22, 2019 at 8:31 AM Abhishek Goel > wrote: >> >> Currently, the cpuidle governors (menu /ladder) determine what idle state >> an idling CPU should enter into based on heuristics that depend on the >> idle history on that CPU. Given that no predictive heuristic is perfect, >> there are cases where the governor predicts a shallow idle state, hoping >> that the CPU will be busy soon. However, if no new workload is scheduled >> on that CPU in the near future, the CPU will end up in the shallow state. >> >> In case of POWER, this is problematic, when the predicted state in the >> aforementioned scenario is a lite stop state, as such lite states will >> inhibit SMT folding, thereby depriving the other threads in the core from >> using the core resources. >> >> To address this, such lite states need to be autopromoted. The cpuidle- >> core can queue timer to correspond with the residency value of the next >> available state. Thus leading to auto-promotion to a deeper idle state as >> soon as possible. > > Isn't the tick stopping avoidance sufficient for that? I was about to ask the same :) -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog