From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MUQyT-0006Fy-MV for qemu-devel@nongnu.org; Fri, 24 Jul 2009 16:02:37 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MUQyO-00069h-Oo for qemu-devel@nongnu.org; Fri, 24 Jul 2009 16:02:37 -0400 Received: from [199.232.76.173] (port=44579 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MUQyO-00069U-KG for qemu-devel@nongnu.org; Fri, 24 Jul 2009 16:02:32 -0400 Received: from mx2.redhat.com ([66.187.237.31]:55767) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1MUQyN-0000GU-TZ for qemu-devel@nongnu.org; Fri, 24 Jul 2009 16:02:32 -0400 Date: Fri, 24 Jul 2009 17:09:27 -0300 From: Glauber Costa Subject: Re: [Qemu-devel] Re: kvm: savevm is broken for me Message-ID: <20090724200927.GE4019@poweredge.glommer> References: <20090723185844.474f7c62@doriath> <20090724105402.1ea81ad5@doriath> <20090724112053.62b67d03@doriath> <60E5AA22-8B6F-488A-BD95-FA3B28935D23@suse.de> <20090724194235.GA19431@poweredge.glommer> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexander Graf Cc: aliguori@us.ibm.com, qemu-devel@nongnu.org, Luiz Capitulino On Fri, Jul 24, 2009 at 09:45:28PM +0200, Alexander Graf wrote: > > On 24.07.2009, at 21:42, Glauber Costa wrote: > >> On Fri, Jul 24, 2009 at 04:27:38PM +0200, Alexander Graf wrote: >>> >>> On 24.07.2009, at 16:20, Luiz Capitulino wrote: >>> >>>> On Fri, 24 Jul 2009 16:18:02 +0200 >>>> Alexander Graf wrote: >>>> >>>>> >>>>> On 24.07.2009, at 15:54, Luiz Capitulino wrote: >>>>> >>>>>> On Fri, 24 Jul 2009 00:06:13 +0200 >>>>>> Alexander Graf wrote: >>>>>> >>>>>>> On 23.07.2009, at 23:58, Luiz Capitulino wrote: >>>>>>> >>>>>>>> >>>>>>>> Hi there, >>>>>>>> >>>>>>>> If I try to 'savevm' with latest Anthony's tree (HEAD >>>>>>>> 6f725c139ae975646c44ace77bf796318a5783da) QEMU will hang and I >>>>>>>> know >>>>>>>> it's not saving anything because vmstat shows no disk activity >>>>>>>> (which >>>>>>>> is the opposite behavior of when 'savevm' works). >>>>>>>> >>>>>>>> According to 'git bisect' the week's winner is: >>>>>>>> >>>>>>>> """ >>>>>>>> commit bd8367761236cd5c435598aeb2f1b8240c09b059 >>>>>>>> Author: Alexander Graf >>>>>>>> Date: Fri Jul 17 13:51:48 2009 +0200 >>>>>>>> >>>>>>>> Fake dirty loggin when it's not there >>>>>>>> """ >>>>>>>> >>>>>>>> Indeed, reverting this makes 'savevm' work for me. >>>>>>> >>>>>>> >>>>>>> Yikes. I have no idea why, but just revert the patch :-). I don't >>>>>>> really need it anymore since we now have dirty logging in PPC. >>>>>>> >>>>>>> Maybe it's the if (is dirty logging really enabled?) in the >>>>>>> beginning? >>>>>> >>>>>> Yes, it's the if. I have removed it and savevm works. >>>>>> >>>>>> Can you submit the fix please? >>>>> >>>>> Eh - what fix? You found that something doesn't set or evaluate the >>>>> flags right. That still doesn't tell us who behaves incorrectly. >>>> >>>> Ah, okay. I thought you meant the 'if' _was_ the bug. >>>> >>>> Better to revert then? >>> >>> Even better yet to find out who's doing something wrong :-). >> >> It's actually quite simple. >> you continue'd instead of break'ing during the dirty log loop, >> which would put us in an infinite loop >> >> Patch follows: > > But who calls kvm_physical_sync_dirty_bitmap with !(mem->flags & > KVM_MEM_LOG_DIRTY_PAGES)? Sounds rather wrong to me. I'd have to dig, but from code inspection, it seems that ram_save_live does it, in its first interaction. This can probably be improved, but I don't think it is wrong semantics anyway. We can sync dirty bitmaps without having mem->flags & KVM_MEM_LOG_DIRTY_PAGES, and just got nothing written to qemu dirty bitmap. Anyway, even if we decide to fix ram_save_live to not do it, getting into an endless loop in that case is buggy. So it is really orthogonal.