From mboxrd@z Thu Jan 1 00:00:00 1970 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Subject: Re: [PATCH 0/2] net: davinci_cpdma: reduce latency on -rt Date: Wed, 27 Jul 2016 16:38:04 +0200 Message-ID: <20160727143804.GC5629@pengutronix.de> References: <1469534545-14478-1-git-send-email-u.kleine-koenig@pengutronix.de> <20160727070302.GG5368@pengutronix.de> <076e6aa6-91f3-8707-1d8b-504c4962f7cd@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Mugunthan V N , linux-omap@vger.kernel.org, netdev@vger.kernel.org, kernel@pengutronix.de To: Grygorii Strashko Return-path: Received: from metis.ext.4.pengutronix.de ([92.198.50.35]:43647 "EHLO metis.ext.4.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756519AbcG0OiK (ORCPT ); Wed, 27 Jul 2016 10:38:10 -0400 Content-Disposition: inline In-Reply-To: <076e6aa6-91f3-8707-1d8b-504c4962f7cd@ti.com> Sender: netdev-owner@vger.kernel.org List-ID: Hello, On Wed, Jul 27, 2016 at 05:11:54PM +0300, Grygorii Strashko wrote: > On 07/27/2016 10:03 AM, Uwe Kleine-K=F6nig wrote: > > On Tue, Jul 26, 2016 at 05:36:49PM +0300, Grygorii Strashko wrote: > >> On 07/26/2016 03:02 PM, Uwe Kleine-K=F6nig wrote: > >>> Hello, > >>> > >>> these patches are based on next-20160726. I didn't check yet how = latency > >>> improves by using these patches, but even if the improvment is sm= all, > >>> it's still a good idea to have them. > >> > >> Sry, but how this will affect on -RT? This is not a raw locks, so > >> they will be converted to rt-mutexes which are sleepable. > >> Or I've missed smth? > >=20 > > They are still locks after all. On -rt I saw for the relevant > > application: > >=20 > > send package | > > take lock | > > write pckt to hw | > > | rcv irq > > | take lock > > | schedule > > drop lock |=20 > > schedule | > > | get pckt from hw > > | drop lock > >=20 > > So reducing the time a lock is taken reduces the chances that the l= ock > > is contended for another thread which results in extra context swit= ches. > >=20 > Thanks a lot for explanation. So, this is not exactly rt-latency redu= ction, > but it might improve net performance on -RT. correct? Well, it's not really rt related, but if you hit a locked lock on rt it hurts more than on !rt. And this results in increased latency. Best regards Uwe --=20 Pengutronix e.K. | Uwe Kleine-K=F6nig = | Industrial Linux Solutions | http://www.pengutronix.de/= |