From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933817AbZJGAzY (ORCPT ); Tue, 6 Oct 2009 20:55:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933666AbZJGAzY (ORCPT ); Tue, 6 Oct 2009 20:55:24 -0400 Received: from mail-yx0-f173.google.com ([209.85.210.173]:52003 "EHLO mail-yx0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932722AbZJGAzX convert rfc822-to-8bit (ORCPT ); Tue, 6 Oct 2009 20:55:23 -0400 MIME-Version: 1.0 In-Reply-To: <1254832609.31336.290.camel@eenurkka-desktop> References: <1254814298.31336.63.camel@eenurkka-desktop> <1254825795.31336.204.camel@eenurkka-desktop> <1254832609.31336.290.camel@eenurkka-desktop> Date: Tue, 6 Oct 2009 17:54:46 -0700 Message-ID: Subject: Re: [BISECTED] "conservative" cpufreq governor broken From: Steven Noonan To: ext-eero.nurkkala@nokia.com Cc: "linux-kernel@vger.kernel.org" , Thomas Gleixner , Rik van Riel , Venkatesh Pallipadi Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Oct 6, 2009 at 5:36 AM, Eero Nurkkala wrote: > On Tue, 2009-10-06 at 13:22 +0200, ext Steven Noonan wrote: >> On Tue, Oct 6, 2009 at 3:43 AM, Eero Nurkkala >> wrote: >> > On Tue, 2009-10-06 at 12:22 +0200, ext Steven Noonan wrote: >> >> >> >> I would suspect you have to have CONFIG_NO_HZ enabled to be able to >> >> reproduce the issue (considering the title of the bisected commit and >> >> my own config). Do you have it enabled? >> >> >> > >> > Yes, it's enabled. >> > >> >> > And another round: >> >> > >> >> > cpufreq stats: OP1:16,78%, OP2:0,24%, OP3:5,14%, OP4:77,83%  (72) >> >> > >> >> > Just once more after doing nothing: >> >> > OP1:7,41%, OP2:0,11%, OP3:2,38%, OP4:90,10%  (82) >> >> > >> >> > So I can't agree it's broken. The patch you bisected, actually filtered >> >> > out such phenomenon, in which an IRQ made the cpufreq framework >> >> > occasionally think we were idling, although we were not. So you got >> >> > "bonus" idle time that shouldn't been there in the first place. Now that >> >> > the "bonus" idle time is not there, your system load may indeed be so >> >> > high that the system never spends 80% or more time in idle? Could that >> >> > be the case? Of course, even though I can't agree it's broken, doesn't >> >> > mean it isn't somehow broken ;) It'd be nice to get info on other >> >> > systems as well... >> >> >> >> Interestingly, "ondemand" (the governor fixed by the bisected commit) >> >> works fine. "conservative" is the only broken one. >> >> >> > >> > If you took timestamps in /arch/x86/kernel/process_**.c: >> > (let's assume process_64.c) in cpu_idle() >> > around enter_idle(); and __exit_idle(), took the diff, >> > added the diffs up, and compared it to system uptime, you could see how >> > much time you spend in idle()? I think it's possible that >> > even if the cpu load is near 0%, the system may idle only for a bare >> > moment (that translates to a buggy pm_idle()), and time is spent >> > elsewhere (less than 80% in idle). >> >> This makes logical sense, but how should I test this? Is there a way >> to do this with existing tracers? > > Tracers may by themselves add some load into the system. > > If I were you, I'd add something like: (I have only one CPU BTW) > > static ktime_t time_prior_idle; > static int64_t idle_total; > > time_prior_idle = ktime_get(); > > idle_total += ktime_to_ns(ktime_sub(ktime_get(), time_prior_idle)); > > and have a sysfs hook (something already present, so you can just cat > it) with a trace: > > printk("Times: %lld, %lld \n", idle_total, ktime_to_ns(ktime_get())); > > Sample output: > 374758812519, 386768249832 > > So I have 386768249832 / 386768249832 = 96.9 % time spent in idle in > this case. > > (Right, this should provide somewhat descent info, hopefully ;) ) > Well, I tried adding the code to cpu_idle() as suggested, but it never printed anything. Apparently cpu_idle() isn't ever being called here. Even added a 'BUG();' at the beginning of the function and it never hit it. Of course, I'm probably missing something obvious. Is there a separate cpu_idle()-esque function for SMP? - Steven