From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Stein Subject: Re: [PATCH v2 00/12] can: rx-offload: add implmentation and switch flexcan driver to use it Date: Wed, 05 Oct 2016 14:37:20 +0200 Message-ID: <1506116.7yduGgf9eG@ws-stein> References: <1467657137-18891-1-git-send-email-mkl@pengutronix.de> <12311540.OPjVtcIYq6@ws-stein> <20161004143315.23423e56@erd980> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: Received: from webbox1416.server-home.net ([77.236.96.61]:59780 "EHLO webbox1416.server-home.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752328AbcJEMhy (ORCPT ); Wed, 5 Oct 2016 08:37:54 -0400 In-Reply-To: <20161004143315.23423e56@erd980> Sender: linux-can-owner@vger.kernel.org List-ID: To: David Jander Cc: Marc Kleine-Budde , linux-can@vger.kernel.org, Martin =?ISO-8859-1?Q?D=E4umler?= , Daniel =?ISO-8859-1?Q?Kr=FCger?= Hi David, On Tuesday 04 October 2016 14:33:15, David Jander wrote: > > In summary the non-RT case seems fine now, but I wonder what causes the > > delays on RT to the CAN-IRQ-Thread which seem to be about 500us (bus time > > of 6 4Byte CAN frames). > > Thanks for testing! > Well, in -RT I guess anything with a higher priority than the CAN-IRQ can > cause a delay... but since going from -rt13 to -rt14 improved the situation, > this sounds like bugs in the -rt code. Are you running any code in > SCHED_FIFO that you don't run in the non-RT case? AFAIK no userspace process is put into SCHED_FIFO and only the priority of CAN-IRQ-Thread is increased to 91. Userspace runs with unchanged priority. So yes I guess there is still problem in -rt code. > It's nevertheless very nice to see that for non-RT, you got from losing > messages to not losing any message with this patchset, even on a lowly > i.MX35 at 1Mbit/s! This proves that the patchset is certainly worth it. I would expect the same from running with RT enabled, especially as the CAN- IRQ-Thread has SCHED_FIFO wuth priority 91. There shouldn't be much code which can delay that thread. Best regards, Alexander