From mboxrd@z Thu Jan 1 00:00:00 1970 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Subject: Re: [RFC 0/4] Improving SPI driver latency (vs v3.8.13.14-rt31) Date: Tue, 9 Sep 2014 22:01:17 +0200 Message-ID: <20140909200117.GU23009@pengutronix.de> References: <1409581835-70814-1-git-send-email-jepler@unpythonic.net> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: linux-rt-users@vger.kernel.org To: Jeff Epler Return-path: Received: from metis.ext.pengutronix.de ([92.198.50.35]:57170 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751102AbaIIUBT (ORCPT ); Tue, 9 Sep 2014 16:01:19 -0400 Content-Disposition: inline In-Reply-To: <1409581835-70814-1-git-send-email-jepler@unpythonic.net> Sender: linux-rt-users-owner@vger.kernel.org List-ID: Hello Jeff, On Mon, Sep 01, 2014 at 09:30:31AM -0500, Jeff Epler wrote: > Unfortunately, I found that there were frequent large latencies, some > over 10ms, when using /dev/spidev. This seems to be typical of other= s' > experience using it (for instance, one can find threads discussing > disappointing RT performance of SPI on the beaglebone and pandaboard;= at > least one raspberry pi project chose to implement a pure userspace SP= I > driver instead of using spidev) >=20 > At all levels of the SPI stack, I found things that could be improved= if > lowest delays are the goal. I doubt that in their current form these > changes are suitable to be incorporated in preempt-rt, but I hope tha= t=20 > this might spur some discussion that would ultimately lead to better > realtime performance of SPI in the preempt-rt kernel. I wonder why you didn't consider mainline as target for your patches instead of preempt-rt. Also you might want to cc the spi maintainer on this topic. I didn't check in detail what you did, but if it's useful for others it would be a pity if it were not picked up because the responsible people were not aware of your effort. Best regards Uwe --=20 Pengutronix e.K. | Uwe Kleine-K=F6nig = | Industrial Linux Solutions | http://www.pengutronix.de/= | -- To unsubscribe from this list: send the line "unsubscribe linux-rt-user= s" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html