From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-x232.google.com (mail-wm0-x232.google.com [IPv6:2a00:1450:400c:c09::232]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3rgzQ24BthzDqhC for ; Sat, 2 Jul 2016 00:32:10 +1000 (AEST) Received: by mail-wm0-x232.google.com with SMTP id a66so31995643wme.0 for ; Fri, 01 Jul 2016 07:32:10 -0700 (PDT) Subject: Re: [PATCH v5] cpuidle: Fix last_residency division To: "Shreyas B. Prabhu" , rjw@rjwysocki.net References: <1467383054-1959-1-git-send-email-shreyas@linux.vnet.ibm.com> Cc: linux-pm@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, nicolas.pitre@linaro.org, bsingharora@gmail.com From: Daniel Lezcano Message-ID: <57767EE6.4080108@linaro.org> Date: Fri, 1 Jul 2016 16:32:06 +0200 MIME-Version: 1.0 In-Reply-To: <1467383054-1959-1-git-send-email-shreyas@linux.vnet.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 07/01/2016 04:24 PM, Shreyas B. Prabhu wrote: > Snooze is a poll idle state in powernv and pseries platforms. Snooze > has a timeout so that if a cpu stays in snooze for more than target > residency of the next available idle state, then it would exit thereby > giving chance to the cpuidle governor to re-evaluate and > promote the cpu to a deeper idle state. Therefore whenever snooze exits > due to this timeout, its last_residency will be target_residency of next > deeper state. > > commit e93e59ce5b85 ("cpuidle: Replace ktime_get() with local_clock()") > changed the math around last_residency calculation. Specifically, while > converting last_residency value from nanoseconds to microseconds it does > right shift by 10. Due to this, in snooze timeout exit scenarios > last_residency calculated is roughly 2.3% less than target_residency of > next available state. This pattern is picked up get_typical_interval() > in the menu governor and therefore expected_interval in menu_select() is > frequently less than the target_residency of any state but snooze. > > Due to this we are entering snooze at a higher rate, thereby affecting > the single thread performance. > > Fix this by using precise division via ktime_us_delta. > > Reported-by: Anton Blanchard > Bisected-by: Shilpasri G Bhat > Signed-off-by: Shreyas B. Prabhu > --- Acked-by: Daniel Lezcano -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog