From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <463B086B.6060402@domain.hid> Date: Fri, 04 May 2007 12:18:19 +0200 From: Gilles Chanteperdrix MIME-Version: 1.0 References: <1178268043.5391.47.camel@domain.hid> In-Reply-To: <1178268043.5391.47.camel@domain.hid> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-help] Latencies while ethernet access List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: CAMUS Benoit Cc: xenomai@xenomai.org CAMUS Benoit wrote: > Hi, > > I'm using Xenomai 2.3.1 with a 2.6.19.2 kernel (from ELDK) on a custom > board based on Xscale PXA processor and with smc91c111 ethernet chip. > I did modifications on Linux kernel to port it on board and then just > applied Adeos's patch following Xenomai's proceedings. > Http and telnet servers are running on and i notice that latencies get > really worse while i access any of them (see traces below). > > I understood that Adeos might avoid that kind of behavior due to its > architecture. So i infer that the ethernet driver might access the > hardware by-passing Adeos ? Despite Adeos architecture, latency with Xenomai is known to depend on the non real-time workload, because there are some low-level ressources such as busses and processor cache that the real-time and non real-time processes need to share. Nevertheless, the latencies you show us are a bit high, this may have several reasons: - maybe you enabled some debugging/statistics options, they have an impact on performance; - the latency of your system may not be properly calibrated, try: echo 25000 > /proc/xenomai/latency - 10ms is a period a bit high, this makes plenty of time for Linux to refill the cache, with a lower period you should observe a lower latency. > In this way and before modificate the driver, i decided to try RT driver > thanks to Rtnet project and get an oops error at device probing due to > memory mapping wich i still don't resolve. > I don't have experience with Xenomai and would apreciate any advice on > that phenomenum. Note that using a real-time driver should rather increase the latency than decrease it, since there will be more unpreemptible critical sections. > I'm a bit surprised too about gap between best and worst latencies so > i'm asking question to myself about my porting, does this gap seam > strange for you too? -- Gilles Chanteperdrix