From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262938AbVF3Kgh (ORCPT ); Thu, 30 Jun 2005 06:36:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262964AbVF3Kew (ORCPT ); Thu, 30 Jun 2005 06:34:52 -0400 Received: from mx2.elte.hu ([157.181.151.9]:57277 "EHLO mx2.elte.hu") by vger.kernel.org with ESMTP id S262938AbVF3KdL (ORCPT ); Thu, 30 Jun 2005 06:33:11 -0400 Date: Thu, 30 Jun 2005 12:32:05 +0200 From: Ingo Molnar To: Kristian Benoit Cc: linux-kernel@vger.kernel.org, paulmck@us.ibm.com, bhuey@lnxw.com, andrea@suse.de, tglx@linutronix.de, karim@opersys.com, pmarques@grupopie.com, bruce@andrew.cmu.edu, nickpiggin@yahoo.com.au, ak@muc.de, sdietrich@mvista.com, dwalker@mvista.com, hch@infradead.org, akpm@osdl.org, rpm@xenomai.org Subject: Re: PREEMPT_RT and I-PIPE: the numbers, take 3 Message-ID: <20050630103205.GA32508@elte.hu> References: <42C320C4.9000302@opersys.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <42C320C4.9000302@opersys.com> User-Agent: Mutt/1.4.2.1i X-ELTE-SpamVersion: MailScanner 4.31.6-itk1 (ELTE 1.2) SpamAssassin 2.63 ClamAV 0.73 X-ELTE-VirusStatus: clean X-ELTE-SpamCheck: no X-ELTE-SpamCheck-Details: score=-4.9, required 5.9, autolearn=not spam, BAYES_00 -4.90 X-ELTE-SpamLevel: X-ELTE-SpamScore: -4 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Kristian Benoit wrote: > This is the 3rd run of our tests. i'm still having problems reproducing your numbers, even the 'plain' ones. I cannot even get the same ballpark figures, on 3 separate systems. To pick one number: > "plain" run: > > Measurements | Vanilla | preemp_rt | > ---------------+-------------+----------------+ > mmap | 660us | 2867us (+334%) | i was unable to reproduce this level of lat_mmap degradation. I do indeed see a slowdown [*], but nowhere near the 4.3x slowdown measured here. I have tried the very lmbench version you used (2.0.4) on 3 different systems (Athlon64 2GHz, Celeron 466MHz, Xeon 2.4GHz - the last one should be pretty similar to your 2.8GHz Xeon testbox) and neither showed this level of slowdown. i couldnt figure out which precise options were used by your test, because i only found the summary lmbench page of one of the older tests - so i did my lat_mmap testing with various sizes: 10MB, 30MB, 70MB, 150MB, 200MB, 500MB. (My best guess would be that since your target box has 512MB of RAM, lmbench will pick an mmap-file size of 144 MB. Or if it's the 256MB box, lmbench will pick roughly 70 MB. I covered those likely sizes too.) Neither size showed this level of slowdown. so my tentative conclusion would be that the -RT kernel is still misconfigured somehow. Did you have HIGHMEM64 and HIGHPTE enabled perhaps? Those i suggested to be turned off in one of my first mails to you, it is something that will cause bad performance under PREEMPT_RT. (Highmem64 is unwarranted for an embedded test anyway - it's only needed to support more than 4 GB of RAM.) Could you send me the test 3 .config you used on the -RT kernel? Ingo [*] fixed in -50-36 and later PREEMPT_RT kernels