From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4CD6DE9F.7000100@domain.hid> Date: Sun, 07 Nov 2010 18:15:11 +0100 From: Gilles Chanteperdrix MIME-Version: 1.0 References: <4CCB4573.30607@domain.hid> <4CD68353.6030600@domain.hid> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-help] High resolution timers disabled on AT91SAM9G20 board after patching List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: at91_enthus Cc: Gilles Chanteperdrix , xenomai@xenomai.org at91_enthus wrote: > Yes, it solved the issue. > > There is one thing that bothers me, though. When I run "xeno-test", the > average and minimal latencies are constant all the time. > > The unpatched version of the xeno kernel seems more consistent when it comes > to minimum, maximum and average latencies. > > I attached a couple of snippets of xeno-test outputs . Do not trust xeno-test too much. Are you sure the only difference between the two runs is the patch, for instance, have you not played with the CONFIG_ARM_FCSE option? Also, good benchmarks are done with running a separate load, and not with xeno-test, in fact. Also, using the high-res timers configuration has a high overhead on such low-end configurations as AT91s, so has CONFIG_PREEMPT. So, if you are looking for a configuration with the lowest overhead possible, I would recommend disabling CONFIG_HIGH_RES_TIMERS and using CONFIG_PREEMPT_NONE or CONFIG_PREEMPT_VOLUNTARY, and relying on Xenomai for the low latency and high resolution timer features. (You can measure the overhead of kernel options with the hackbench test for instance). On the AT91 I have (AT91SAM9263), the minimum and average latencies oscillate much less than for your unpatched kernel, either with or without the patch so I wonder if you would not have another issue. Do you have FCSE enabled? To give you an idea of the figures here, with FCSE enabled, the minimal latency is around 15us and the average latency around 50us. And they vary in a 5us range, they do not make big jumps. -- Gilles.