From mboxrd@z Thu Jan 1 00:00:00 1970 From: Armin Steinhoff Subject: Re: Interrupt Bottom Half Scheduling Date: Tue, 15 Feb 2011 09:40:22 +0100 Message-ID: <4D5A3BF6.6090008@steinhoff.de> References: Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: linux-rt-users@vger.kernel.org To: Peter LaDow Return-path: Received: from moutng.kundenserver.de ([212.227.17.8]:59598 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754507Ab1BOIfA (ORCPT ); Tue, 15 Feb 2011 03:35:00 -0500 In-Reply-To: Sender: linux-rt-users-owner@vger.kernel.org List-ID: Hi, the scheduling is done by the CFS ? --Armin Peter LaDow wrote: > 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 priority >>> of 50. But when running a priority 99 thread, we still seem to be >>> getting interrupted. Shouldn't the hrtimer softirq be put off until >>> the CPU is idle or a lower priority task is running? >> Is the hrtimer softirq executing when the priority 99 thread is spinning >> in it's for loop? Your "jitter Due to Large Number of Timers" email >> 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. 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-users" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >