From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter LaDow Subject: Re: Interrupt Bottom Half Scheduling Date: Mon, 14 Feb 2011 15:08:58 -0800 Message-ID: References: <1297724643.10271.16.camel@quadrophenia> 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: Sven-Thorsten Dietrich Return-path: Received: from mail-yx0-f174.google.com ([209.85.213.174]:46080 "EHLO mail-yx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751882Ab1BNXI7 convert rfc822-to-8bit (ORCPT ); Mon, 14 Feb 2011 18:08:59 -0500 Received: by yxt3 with SMTP id 3so2296604yxt.19 for ; Mon, 14 Feb 2011 15:08:58 -0800 (PST) In-Reply-To: <1297724643.10271.16.camel@quadrophenia> Sender: linux-rt-users-owner@vger.kernel.org List-ID: Note sure how that is possible. This is related to my earlier posting about timing jitter. Our code is basically this: while(1) { t1 =3D clock_gettime() for(i=3D0; i < 10000; i++) t2 =3D clock_gettime() diff =3D t2 - 1 } This task is pending on nothing. Unless clock_gettime() causes some sort of priority inversion, I don't see the problem. We see significant jitter on the for-loop when there are a significant number of other kernel timers. Now, as we understand it, the hrtimers run in the softirq. But if the softirq is priority 50, and this for-loop is priority 99, it shouldn't be affected by the softirq thread. Pete On Mon, Feb 14, 2011 at 3:04 PM, Sven-Thorsten Dietrich wrote: > On Mon, 2011-02-14 at 14:31 -0800, Peter LaDow wrote: >> How is the scheduling of the hrtimers softirq thread handled? >> >> When querying the RT priority of the hrtimer softirq, I get a priori= ty >> of 50. =A0But when running a priority 99 thread, we still seem to be >> getting interrupted. =A0Shouldn't the hrtimer softirq be put off unt= il >> the CPU is idle or a lower priority task is running? > > Does your prio 99 thread perhaps encounter a prio inversion dependenc= y > on one of the softriq threads? > >> >> Thanks, >> Pete >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-rt-u= sers" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at =A0http://vger.kernel.org/majordomo-info.html > > > -- 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