From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: 2.6.35-rc2-git2: Reported regressions from 2.6.34 Date: Fri, 11 Jun 2010 21:53:06 +0200 Message-ID: <4C129422.1010900@fusionio.com> References: <4C0F4872.7090909@fusionio.com> <20100611083249.GA11143@elte.hu> <4C11F661.3070604@fusionio.com> <20100611085520.GA20218@elte.hu> <4C11FF77.1000101@fusionio.com> <20100611190714.GA20837@redhat.com> <4C128A75.3030501@fusionio.com> <20100611194849.GB20837@redhat.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20100611194849.GB20837-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> Sender: kernel-testers-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Vivek Goyal Cc: Ingo Molnar , Linus Torvalds , "Rafael J. Wysocki" , Carl Worth , Eric Anholt , Divyesh Shah , "guijianfeng-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org" , Linux Kernel Mailing List , Andrew Morton , Kernel Testers List On 11/06/10 21.48, Vivek Goyal wrote: > On Fri, Jun 11, 2010 at 09:11:49PM +0200, Jens Axboe wrote: >> On 11/06/10 21.07, Vivek Goyal wrote: >>> On Fri, Jun 11, 2010 at 11:18:47AM +0200, Jens Axboe wrote: >>>> On 2010-06-11 10:55, Ingo Molnar wrote: >>>>>>> Caused by the same blkiocg_update_io_add_stats() function. Bootlog and config >>>>>>> attached. Reproducible on that sha1 and with that config. >>>>>> >>>>>> I think I see it, the internal CFQ blkg groups are not properly >>>>>> initialized... Will send a patch shortly. >>>>> >>>>> Cool - can test it with a short turnaround, the bug is easy to reproduce. >>>> >>>> Here's a nasty patch that should fix it. Not optimal, since we really >>>> just want empty functions for these when cfq group scheduling is not >>>> defined. >>>> >>>> CC'ing the guilty parties to come up with a better patch that does NOT >>>> involve ifdefs in cfq-iosched.c. We want blk-cgroup.[ch] fixed up. >>>> And trimming the CC list a bit. >>> >>> Jens, Ingo, I am sorry for this mess. >>> >>> Jens, >>> >>> How about introducing "block/cfq.h" and declaring additional set of wrapper >>> functions to update blkiocg stats and make these do nothing if >>> CFQ_GROUP_IOSCHED=n. >>> >>> For example, in linux-2.6/block/cfq.h, we can define functions as follows. >>> >>> #ifdef CONFIG_CFQ_GROUP_IOSCHED >>> cfq_blkiocg_update_dequeue_stats () { >>> blkiocg_update_dequeue_stats() >>> } >>> #else >>> cfq_blkiocg_update_dequeue_stats () {} >>> #endif >>> >>> Fixing it blk-cgroup.[ch] might not be best as BLK_CGROUP is set. >>> Secondly, if there are other IO control policies later, they might >>> want to make use of BLK_CGROUP while cfq has disabled the group io >>> scheduling. >> >> I already tried such a patch, but it's not exactly pretty. How about >> splitting blk-cgroup.c into two parts, one that is built for >> BLK_CGROUP and an additional one that is also built for >> CFQ_GROUP_SCHED? Lets try and improve on the ifdef mess, not extend >> it. > > Sorry, I did not understand your suggestion. Can you please throw some more > light on it. > > blk-cgroup.c does not have any cfq specific parts. So I can't split it > out and build part of it based on CFQ_GROUP_SCHED. I know they are not cfq specific, but cfq is the only one that calls them currently. If others depend on them later on, then let that other blk-cgroup-iosched.o be built for them as well. -- Jens Axboe