From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnaldo Carvalho de Melo Subject: Re: RT_PREEMPT and Serial Port Date: Sun, 13 Apr 2008 15:56:48 -0300 Message-ID: <20080413185648.GC11343@ghostprotocols.net> References: <20080404075753.GB28260@alumnos.inf.utfsm.cl> <20080412200837.GA6223@mgross-t43> <20080412233428.GA4261@alumnos.inf.utfsm.cl> <20080413180007.GA4955@mgross-t43> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Mauricio =?utf-8?Q?A=2E_Araya_L=EF=BF=BDpez?= , linux-rt-users@vger.kernel.org To: mgross <640e9920@gmail.com> Return-path: Received: from mx1.redhat.com ([66.187.233.31]:40182 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752527AbYDMS45 (ORCPT ); Sun, 13 Apr 2008 14:56:57 -0400 Content-Disposition: inline In-Reply-To: <20080413180007.GA4955@mgross-t43> Sender: linux-rt-users-owner@vger.kernel.org List-ID: Em Sun, Apr 13, 2008 at 11:00:08AM -0700, mgross escreveu: > On Sat, Apr 12, 2008 at 07:34:28PM -0400, Mauricio A. Araya L=EF=BF=BD= pez wrote: > > On Sat, Apr 12, 2008 at 01:08:37PM -0700, mgross wrote: > > > On Fri, Apr 04, 2008 at 03:57:53AM -0400, Mauricio A. Araya L=EF=BF= =BDpez wrote: > > > > Hi all, > > > >=20 > > > > I've been searching on the web (and in the rt-wiki) for the cur= rent > > > > status of the real-time support for devices. For instance > > > > the serial port, CAN Bus, etc. > > > >=20 > > [...] > >=20 > > > FWIW I was able to get +/- 30usec jitter from a serial port exper= iment > > > where I programmed a PIC to push 5 bytes over the serial line eve= ry > > > 20ms.=20 > > My results are similar. A 30 usec jitter it seems to be the limit, > > but indeed the jitter is less, because the latency is near the > > 10 usec. But, that is "on average", because I've run several > > test during long time periods, and my worst jitter is like 5 msec!, > > which is too much. Maybe it is a hardware problem, but I am using > > no swap, no usb and no DMA, and I dont know which other thing > > i should disable to not have this huge random jitter. > > (Obviosly I am locking the memory to have no paging) >=20 > How long did you need to run it to hit a 5msec jitter? >=20 > My tests where only for a few min while I test compiled the kernel a > few times to see if that would effect things. And have you guys tried with a ftrace/latency trace enabled kernel? It would be really interesting to know what happens in this 5ms :-) - Arnaldo -- 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