From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <471753AA.20709@domain.hid> Date: Thu, 18 Oct 2007 14:38:02 +0200 From: "CHABAL David" MIME-Version: 1.0 References: <4705ED3B.4070600@domain.hid> <2ff1a98a0710050130j7e0db84dq838aab0417c8bd3f@domain.hid> <4705FE04.7000909@domain.hid> <1191576011.20623.114.camel@domain.hid> <470611FA.30103@domain.hid> <1191592977.20623.142.camel@domain.hid> <470A26BC.506@domain.hid> <1192015852.22917.197.camel@domain.hid> <470F7F2E.3020206@domain.hid> <470F82FF.9020701@domain.hid> <1192203284.6499.135.camel@domain.hid> <470F978B.1000005@domain.hid> <1192207431.6499.161.camel@domain.hid> <4715C70F.4040501@domain.hid> <1192610471.5973.4.camel@domain.hid> <4715CE15.10202@domain.hid> <1192612658.5973.11.camel@domain.hid> <47160AD3.4090109@domain.hid> <1192628763.5973.16.camel@domain.hid> <471621C8.9070006@domain.hid> <1192634673.5973.33.camel@domain.hid> <47162E66.1080406@domain.hid> <1192637158.5973.51.camel@domain.hid> In-Reply-To: <1192637158.5973.51.camel@domain.hid> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable Subject: Re: [Xenomai-help] awful latencies (~110us) List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: rpm@xenomai.org Cc: xenomai@xenomai.org Philippe Gerum a =E9crit : > On Wed, 2007-10-17 at 17:46 +0200, CHABAL David wrote: >> Philippe Gerum a =E9crit : >>> On Wed, 2007-10-17 at 16:52 +0200, CHABAL David wrote: >>>>> Grmmff... I think the PIC on this box has some deep troubles; pleas= e try >>>>> this patch, in replacement of the previous ipipe_trace_special >>>>> instrumentation: >>>>> >>>> RTD| 8.348| 10.387| 43.647| 0| 6.098|=20 >>>> 80.440 >>>> ---|------------|------------|------------|--------|----------------= --------- >>>> RTS| 6.098| 10.020| 80.440| 0| 00:17:20/00:= 17:20 >>>> [root@domain.hid bin]# >>>> >>>> >>>> IRQ handling takes 17=B5s in the worst case. >>>> >>>> It takes a long time to write 3 poor bytes... >>>> >>> Indeed. Each outb to the ISA bus should be somewhere in the 1-2.5 us >>> range depending on the hw, maybe a bit higher in case of contention, = but >>> not that much. >>> >>>> May be is it a SMI problem ??? (Globally disable SMI is on) >>>> >>> It's less likely with an ICH-2 chipset. >>> >>> I see that CONFIG_IDEDMA_PCI_AUTO is disabled. Any reason not to use = PCI >>> DMA when available for IDE drives with your hw? >>> >> I read this about DMA: >> http://www.rtai.dk/cgi-bin/gratiswiki.pl?DMA_And_Jitter >> >=20 > As usual, usage of DMA in real-time situations is a trade-off, and > should be evaluated within the context of the hw at hand. DMA does bus > mastering, but OTOH, forcing PIO raises native Linux latencies, which > also has some drawbacks for real-time kernels implementing RT/non-RT > mode transitions for tasks like Xenomai and RTAI do. For this reason, > you may want to try switching PCI DMA on for your platform, until it > does prove bad latency-wise. >=20 I tested it but the results are almost the same. I will try to upgrade my kernel to the 2.6.22 and to test again. David