From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4FBC0383.3020608@bbn.com> Date: Tue, 22 May 2012 17:22:11 -0400 From: Mitchell Tasman MIME-Version: 1.0 References: <4FBADE7D.5030609@bbn.com> <4FBB4951.5070803@xenomai.org> In-Reply-To: <4FBB4951.5070803@xenomai.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai] A possible mis-interaction between CONFIG_PREEMPT and GPIO IRQ handling for ARM, leading to extreme latency List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: xenomai@xenomai.org Gilles, On 05/22/2012 04:07 AM, Gilles Chanteperdrix wrote: > On 05/22/2012 02:31 AM, Mitchell Tasman wrote: >> Hi. I'm running an OMAP DM3725-based board with a 2.6.38.8 kernel, a >> mid-May 2012 git snapshot of xenomai-2.6, and a backport (really just >> application) of the patch that Gilles referenced in the "IRQ latency" >> thread last week: >> >> http://git.xenomai.org/?p=ipipe-gch.git;a=commit;h=81bfc05c4716b76e79f5e486baf4c52015a3b92c > > Please try the following patch instead: Thank you very much for your prompt and most helpful response. I have applied the patch that you supplied, and find a dramatic reduction in the maximum latency experienced in servicing edge-triggered GPIO interrupts. In testing so far today with the new patch, I have not encountered a single instance of the sort of extreme latency that prompted my query to the mailing list. Might you consider applying the new patch to I-Pipe for ARM 2.6.38.8, and publishing a new revision of that patch set? This could be of significant benefit to those members of the Xenomai community that are presently using a 2.6.38.8 kernel on ARM platforms. You might also consider addressing/replacing the original "ipipe/arm: defer chained interrupts handling" patch that was applied to I-Pipe for ARM 3.0.13, if the new patch is relevant to that kernel as well. Thanks again and Best Regards, Mitch