From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-x241.google.com (mail-wm0-x241.google.com [IPv6:2a00:1450:400c:c09::241]) (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 3rjmMP4KCrzDqnw for ; Mon, 4 Jul 2016 22:21:05 +1000 (AEST) Received: by mail-wm0-x241.google.com with SMTP id 187so21302217wmz.1 for ; Mon, 04 Jul 2016 05:21:05 -0700 (PDT) MIME-Version: 1.0 Sender: rjwysocki@gmail.com In-Reply-To: <5102d9f9-3b38-17c3-98ce-cceb073da764@gmail.com> References: <1467383054-1959-1-git-send-email-shreyas@linux.vnet.ibm.com> <5102d9f9-3b38-17c3-98ce-cceb073da764@gmail.com> From: "Rafael J. Wysocki" Date: Mon, 4 Jul 2016 14:20:59 +0200 Message-ID: Subject: Re: [PATCH v5] cpuidle: Fix last_residency division To: Balbir Singh , "Shreyas B. Prabhu" , Daniel Lezcano Cc: "Rafael J. Wysocki" , Linux PM , linuxppc-dev , Nicolas Pitre Content-Type: text/plain; charset=UTF-8 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, Jul 4, 2016 at 8:10 AM, Balbir Singh wrote: > > > On 02/07/16 00:24, 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 >> --- > > This looks so much cleaner :) > > Acked-by: Balbir Singh Patch applied, thanks!