From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <439077A7.6000903@domain.hid> Date: Fri, 02 Dec 2005 17:34:47 +0100 From: Philippe Gerum MIME-Version: 1.0 Subject: Re: [Xenomai-help] i386 2.4 backport performing (too?) well References: <4390470F.8040503@domain.hid> <439071EF.3040004@domain.hid> In-Reply-To: <439071EF.3040004@domain.hid> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Wolfgang Grandegger Cc: xenomai@xenomai.org Wolfgang Grandegger wrote: > Jan Kiszka wrote: > >> Klaas Gadeyne wrote: >> >>> With the arrival of the 2.4 i386 adeos ipipe patch for xenomai [1], I >>> decided to try to compile xenomai-trunk for a 2.4 kernel. This worked >>> flawlessly, and moreover, I got excellent latency results: >>> >>> I used the "same" kernel config as for our 2.4.31 rtai3.0r5 kernel, >>> which is based on Takis Issaris' liveCD config. >>> >>> This resulted in a maximal latency of 30 usec after a run of over 100 >>> minutes under heavy load (tar and dd loops, compiling, keyboard >>> interrupts and ping flood) [2]. >>> >>> For comparison, on the same hardware platform: - the RTAI lxrt-latency >>> on rtai 3.0r5 (adeos oldgen r18c1 >>> patch for 2.4.31 also) test reports 38 usec >>> - the latency test of xenomai 2.01 running on a 2.6.14-ipipe-1.0-10 >>> kernel resulted in a latency of 80 usec. >>> >>> This seems too good to be true? Can one simply compare the results of >>> the former RTAI lxrt-latency test with the xenomai latency test? >> >> >> >> Mmh, I tend to be sceptical as well, also remembering the results >> Wolfgang posted about 2.6 vs. 2.4 on low-end PPC >> (https://mail.gna.org/public/xenomai-core/2005-11/msg00131.html). >> >> Well, such worst-case improvement may be real if and only if there is >> less *kernel* code in hard-irq-off sections with 2.4. The complexity of >> adeos/ipipe and xenomai isn't changed between both scenarios. >> >> But I rather think that 2.4 just stresses the caches less than 2.6, thus >> is may be more tricky to trigger the real worst-case path. So, what we >> already saw with PPC: 2.4 and 2.6 may likely show similar RT >> performances under Xenomai, but the overall system performance is much >> better on low-end! However, I would be happy if this theory is too >> pessimistic. > > > In the meantime I have measured latencies a few PowerPC systems with > Xenomai 2.1 under Linux 2.4 and 2.6 and RTAI 3.0r5 (using RTHAL) under > 2.4. The latency figures for Xenomai compared with RTAI 3.0r5 are > roughly a factor of two worse but I have not realized a significant > difference between 2.4 and 2.6 (with Xenmomai, of course). We still need to compare pure kernel-space executions since RTAI does not support user-space for PPC, but v2.1 does not provide the kernel space test yet, due to the build system refactoring. Still pondering how to introduce this back into the codebase. > > Wolfgang. > > _______________________________________________ > Xenomai-help mailing list > Xenomai-help@domain.hid > https://mail.gna.org/listinfo/xenomai-help > -- Philippe.