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Message-ID: <20160727143804.GC5629@pengutronix.de> Date: Wed, 27 Jul 2016 16:38:04 +0200 From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de> To: Grygorii Strashko <grygorii.strashko@...com> Cc: Mugunthan V N <mugunthanvnm@...com>, linux-omap@...r.kernel.org, netdev@...r.kernel.org, kernel@...gutronix.de Subject: Re: [PATCH 0/2] net: davinci_cpdma: reduce latency on -rt Hello, On Wed, Jul 27, 2016 at 05:11:54PM +0300, Grygorii Strashko wrote: > On 07/27/2016 10:03 AM, Uwe Kleine-König wrote: > > On Tue, Jul 26, 2016 at 05:36:49PM +0300, Grygorii Strashko wrote: > >> On 07/26/2016 03:02 PM, Uwe Kleine-König 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 small, > >>> 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? > > > > They are still locks after all. On -rt I saw for the relevant > > application: > > > > send package | > > take lock | > > write pckt to hw | > > | rcv irq > > | take lock > > | schedule > > drop lock | > > schedule | > > | get pckt from hw > > | drop lock > > > > So reducing the time a lock is taken reduces the chances that the lock > > is contended for another thread which results in extra context switches. > > > Thanks a lot for explanation. So, this is not exactly rt-latency reduction, > 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 -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ |
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