From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <456EE120.5060003@domain.hid> Date: Thu, 30 Nov 2006 14:48:16 +0100 From: Markus Franke MIME-Version: 1.0 Subject: Re: [Xenomai-help] measuring context switch primary<->secondary mode References: <456D5075.1060905@domain.hid> <200611301119.01173.schwab@domain.hid> In-Reply-To: <200611301119.01173.schwab@domain.hid> Content-Type: multipart/mixed; boundary="------------080601060802090508070506" Reply-To: Markus.Franke@domain.hid List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Ulrich Schwab Cc: xenomai@xenomai.org This is a multi-part message in MIME format. --------------080601060802090508070506 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Ulrich Schwab wrote: > I think that CONFIG_PREEMPT should reduce the jitter of Your measurement, most > importantly the worst case switch time, for wich You need a long test run > under heavy load. > CONFIG_PREEMPT is there to provide more determinism, which usually has a price > in performance. > Realtime is about determinism not performance (or speed). > Its not maximum speed but guaranteed minimum speed. You are absolutely right. I put my system under some load (dd) and made two tests. One was with CONFIG_PREEMPT and one without. The worst case switch time jitter was about 30% lower in the CONFIG_PREEMPT case, so your prediction was right. > Since the probability of a preemption during the mode switch without > CONFIG_PREEMPT is lower, it might take a long time until the worst case mode > switch time is observed. Sorry but I don't understand what you are meaning. Let me explain my point of view. When a realtime task in the Xenomai-Domain makes a linux-systemcall the task is migrated fully automatically to the Linux-Domain as soon as we reach the next preemption point in the Linux-Kernel. Due to the fact that preemptability of the linux-kernel increase when using CONFIG_PREEMPT, the time to the next preemption point should decrease, right? I don't get the point of your last sentence. Thanks for help, Markus Franke -- Nichts ist so praktisch wie eine gute Theorie! --------------080601060802090508070506 Content-Type: text/x-vcard; charset=utf-8; name="Markus.Franke.vcf" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="Markus.Franke.vcf" YmVnaW46dmNhcmQNCmZuOk1hcmt1cyBGcmFua2UNCm46RnJhbmtlO01hcmt1cw0KYWRyO3F1 b3RlZC1wcmludGFibGU6OztWZXR0ZXJzc3RyYT1DMz05RmUgNjQvNzIyO0NoZW1uaXR6O1Nh eG9ueTswOTEyNjtHZXJtYW55DQplbWFpbDtpbnRlcm5ldDpNYXJrdXMuRnJhbmtlQGluZm9y bWF0aWsudHUtY2hlbW5pdHouZGUNCngtbW96aWxsYS1odG1sOkZBTFNFDQp1cmw6aHR0cDov L3d3dy50dS1jaGVtbml0ei5kZS9+ZnJhbm0NCnZlcnNpb246Mi4xDQplbmQ6dmNhcmQNCg0K --------------080601060802090508070506--