From mboxrd@z Thu Jan 1 00:00:00 1970 Received: by rv-out-0708.google.com with SMTP id f25so4823386rvb.26 for ; Mon, 28 Jul 2008 08:30:34 -0700 (PDT) Message-ID: <2c0942db0807280830n621922vdb5e9fdb6c66d48f@mail.gmail.com> Date: Mon, 28 Jul 2008 08:30:34 -0700 From: "Ray Lee" Subject: Re: PERF: performance tests with the split LRU VM in -mm In-Reply-To: <20080728105742.50d6514e@cuia.bos.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <20080724222510.3bbbbedc@bree.surriel.com> <20080728105742.50d6514e@cuia.bos.redhat.com> Sender: owner-linux-mm@kvack.org Return-Path: To: Rik van Riel Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org List-ID: On Mon, Jul 28, 2008 at 7:57 AM, Rik van Riel wrote: > On Thu, 24 Jul 2008 22:25:10 -0400 > Rik van Riel wrote: > >> TEST 1: dd if=/dev/sda of=/dev/null bs=1M >> >> kernel speed swap used >> >> 2.6.26 111MB/s 500kB >> -mm 110MB/s 59MB (ouch, system noticably slower) >> noforce 111MB/s 128kB >> stream 108MB/s 0 (slight regression, not sure why yet) >> >> This patch shows that the split LRU VM in -mm has a problem >> with large streaming IOs: the working set gets pushed out of >> memory, which makes doing anything else during the big streaming >> IO kind of painful. >> >> However, either of the two patches posted fixes that problem, >> though at a slight performance penalty for the "stream" patch. > > OK, the throughput number with this test turns out not to mean > nearly as much as I thought. > > Switching off CPU frequency scaling, pinning the CPUs at the > highest speed, resulted in a throughput of only 102MB/s. > > My suspicion is that faster running code on the CPU results > in IOs being sent down to the device faster, resulting in > smaller IOs and lower throughput. Or the IOs are getting sent in a different order, and so coalescing/merging isn't occurring as often. Getting some instrumentation (something as simple as a histogram) on the IO sizes could be useful. -- 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/ . Don't email: email@kvack.org