From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [RFC PATCH] kick ksoftirqd more often to please soft lockup detector Date: Sat, 3 Mar 2012 00:39:02 -0800 Message-ID: <20120303083902.GC8270@linux.vnet.ibm.com> References: <20120227203847.22153.62468.stgit@dwillia2-linux.jf.intel.com> <1330422535.11248.78.camel@twins> <1330507023.11248.113.camel@twins> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from e38.co.us.ibm.com ([32.97.110.159]:46622 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750863Ab2CCIjG (ORCPT ); Sat, 3 Mar 2012 03:39:06 -0500 Received: from /spool/local by e38.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sat, 3 Mar 2012 01:39:06 -0700 Content-Disposition: inline In-Reply-To: <1330507023.11248.113.camel@twins> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Peter Zijlstra Cc: Dan Williams , Thomas Gleixner , linux-kernel@vger.kernel.org, Jens Axboe , linux-scsi@vger.kernel.org, Lukasz Dorau , James Bottomley , Andrzej Jakowski On Wed, Feb 29, 2012 at 10:17:03AM +0100, Peter Zijlstra wrote: > On Tue, 2012-02-28 at 14:16 -0800, Dan Williams wrote: > > Looks like everyone is guilty: > > > > [ 422.765336] softirq took longer than 1/4 tick: 3 NET_RX ffffffff813f0aa0 > > ... > > [ 423.971878] softirq took longer than 1/4 tick: 4 BLOCK ffffffff812519c8 > > [ 423.985093] softirq took longer than 1/4 tick: 6 TASKLET ffffffff8103422e > > [ 423.993157] softirq took longer than 1/4 tick: 7 SCHED ffffffff8105e2e1 > > [ 424.001018] softirq took longer than 1/4 tick: 9 RCU ffffffff810a0fed > > [ 424.008691] softirq loop took longer than 1/2 tick need_resched: > > /me kicks himself for not printing the actual duration.. :-) > > > As expected whenever that 1/2 tick message gets emitted the softirq > > handler is almost running in a need_resched() context. > > Yeah.. that's quite expected. > > > So is it a good idea to get more aggressive about scheduling ksoftrrqd? > > Nah, moving away from softirq more like. I'll put moving the > load-balancer into a kthread on the todo list. And it looks like > everybody else should move to kthreads too. Last year when I tried that, things got a bit ugly. I guess I don't need the kthreads to be realtime unless CONFIG_RCU_BOOST=y, maybe that will help. Also IIRC Steven Rostedt made some real-time changes that might help as well for my case, which would have a per-CPU RT kthread. Thanx, Paul