From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH 00/13] IO-less dirty throttling v2 Date: Wed, 17 Nov 2010 23:33:50 -0800 Message-ID: <20101117233350.321f9935.akpm@linux-foundation.org> References: <20101117042720.033773013@intel.com> <20101117150330.139251f9.akpm@linux-foundation.org> <20101118020640.GS22876@dastard> <20101117180912.38541ca4.akpm@linux-foundation.org> <20101118032141.GP13830@dastard> <20101117193431.ec1f4547.akpm@linux-foundation.org> <20101118072706.GW13830@dastard> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Wu Fengguang , Jan Kara , Christoph Hellwig , "Theodore Ts'o" , Chris Mason , Peter Zijlstra , Mel Gorman , Rik van Riel , KOSAKI Motohiro , linux-mm , linux-fsdevel@vger.kernel.org, LKML To: Dave Chinner Return-path: In-Reply-To: <20101118072706.GW13830@dastard> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Thu, 18 Nov 2010 18:27:06 +1100 Dave Chinner wrote: > > > Indeed, nobody has > > > realised (until now) just how inefficient it really is because of > > > the fact that the overhead is mostly hidden in user process system > > > time. > > > > "hidden"? You do "time dd" and look at the output! > > > > _now_ it's hidden. You do "time dd" and whee, no system time! > > What I meant is that the cost of foreground writeback was hidden in > the process system time. Now we have separated the two of them, we > can see exactly how much it was costing us because it is no longer > hidden inside the process system time. About a billion years ago I wrote the "cyclesoak" thingy which measures CPU utilisation the other way around: run a lowest-priority process on each CPU in the background, while running your workload, then find out how much CPU time cyclesoak *didn't* consume. That way you account for everything: user time, system time, kernel threads, interrupts, softirqs, etc. It turned out to be pretty accurate, despite the then-absence of SCHED_IDLE. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org