Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754522Ab3HRRKj (ORCPT ); Sun, 18 Aug 2013 13:10:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:10372 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753544Ab3HRRKi (ORCPT ); Sun, 18 Aug 2013 13:10:38 -0400 Date: Sun, 18 Aug 2013 19:04:08 +0200 From: Oleg Nesterov To: Frederic Weisbecker , "Rafael J. Wysocki" , Viresh Kumar , Stratos Karafotis Cc: LKML , Fernando Luis Vazquez Cao , Tetsuo Handa , Thomas Gleixner , Ingo Molnar , Peter Zijlstra , Andrew Morton , Arjan van de Ven Subject: Re: [PATCH 1/4] nohz: Only update sleeptime stats locally Message-ID: <20130818170408.GA22417@redhat.com> References: <1376667753-29014-1-git-send-email-fweisbec@gmail.com> <1376667753-29014-2-git-send-email-fweisbec@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1376667753-29014-2-git-send-email-fweisbec@gmail.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2106 Lines: 59 Sorry for double post. forgot to cc cpufreq maintainers. On 08/16, Frederic Weisbecker wrote: > > To fix this, lets only update the sleeptime stats locally when the CPU > exits from idle. I am in no position to ack the changes in this area, but I like this change very much. Because, as a code reader, I was totally confused by if (last_update_time) update_ts_time_stats() code and it looks "obviously wrong". I added more cc's. It seems to me that 9366d840 "cpufreq: governors: Calculate iowait time only when necessary" doesn't realize what - u64 idle_time = get_cpu_idle_time_us(cpu, NULL); + u64 idle_time = get_cpu_idle_time_us(cpu, io_busy ? wall : NULL); actually means. OTOH, get_cpu_iowait_time_us() was called with last_update_time != NULL even before this patch... In short. This looks like the clear fix to me, but I do not understand this code enough, and I think that cpufreq should know about this change. > static void tick_nohz_stop_idle(int cpu, ktime_t now) > { > struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); > + ktime_t delta; > > - update_ts_time_stats(cpu, ts, now, NULL); > + /* Updates the per cpu time idle statistics counters */ > + delta = ktime_sub(now, ts->idle_entrytime); > + if (nr_iowait_cpu(cpu) > 0) > + ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta); > + else > + ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); > + ts->idle_entrytime = now; > ts->idle_active = 0; With or without this change, why we update ->idle_entrytime in this case? Looks harmless, but a bit confusing. While this doesn't really matter, we could probably even kill ->idle_active and use !!ts->idle_entrytime instead. > @@ -473,17 +458,14 @@ u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) And I think that we should kill this last_update_time argument later. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/