From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter LaDow Subject: Re: Interrupt Bottom Half Scheduling Date: Mon, 14 Feb 2011 17:10:05 -0800 Message-ID: References: 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: Frank Rowand Return-path: Received: from mail-gy0-f174.google.com ([209.85.160.174]:48951 "EHLO mail-gy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751082Ab1BOBKH convert rfc822-to-8bit (ORCPT ); Mon, 14 Feb 2011 20:10:07 -0500 Received: by gyb11 with SMTP id 11so2337772gyb.19 for ; Mon, 14 Feb 2011 17:10:06 -0800 (PST) In-Reply-To: Sender: linux-rt-users-owner@vger.kernel.org List-ID: On Mon, Feb 14, 2011 at 3:30 PM, Frank Rowand = wrote: > On Mon, Feb 14, 2011 at 2:31 PM, 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? > > Is the hrtimer softirq executing when the priority 99 thread is spinn= ing > in it's for loop? =A0Your "jitter Due to Large Number of Timers" emai= l > said that the lower priority tasks don't seem to be interrupting the > priority 99 thread. Did I? Hmm, well I mean the lower priority task with 100 threads. At least I think so. It is hard to tell. It seems to me that the softirq thread is the source of the problem. Since the tight loop is getting such a variety of times (400us of jitter only while the other process is running) that it does seem that the loop is getting interrupt. > The hardware timer interupts will interrupt the priority 99 thread. =A0= The > cost of these interrupts and the resultant calls to try_to_wake_up() > of the hrtimer softirq might be quite large considering the rate of > timer expires you mentioned in your first email. Sure, we expect the timer interrupt to interfere. But as we understand it, the softirq is what schedules the task switch. The top half only schedules the bottom half. But since the bottom half is priority 50, there shouldn't be any interruption of the priority 99 expect to handle the low level IRQ. > Out of curiosity, is the system UP or SMP? UP. Just a single MPC5349. pete -- 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