From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Xu Subject: Re: [PATCH] migration: introduce decompress-error-check Date: Wed, 2 May 2018 11:03:09 +0800 Message-ID: <20180502030309.GC25938@xz-mi> References: <20180426091519.26934-1-xiaoguangrong@tencent.com> <32eaad8e-35a0-5240-37a2-4242b7890ab9@redhat.com> <20180427093135.GC13269@xz-mi> <2f84ab90-2b9c-9888-e6e2-9114ae046078@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: kvm@vger.kernel.org, mst@redhat.com, mtosatti@redhat.com, Xiao Guangrong , qemu-devel@nongnu.org, dgilbert@redhat.com, wei.w.wang@intel.com, jiang.biao2@zte.com.cn, pbonzini@redhat.com To: Xiao Guangrong Return-path: Content-Disposition: inline In-Reply-To: <2f84ab90-2b9c-9888-e6e2-9114ae046078@gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel2=m.gmane.org@nongnu.org Sender: "Qemu-devel" List-Id: kvm.vger.kernel.org On Fri, Apr 27, 2018 at 06:40:09PM +0800, Xiao Guangrong wrote: > > > On 04/27/2018 05:31 PM, Peter Xu wrote: > > On Fri, Apr 27, 2018 at 11:15:37AM +0800, Xiao Guangrong wrote: > > > > > > > > > On 04/26/2018 10:01 PM, Eric Blake wrote: > > > > On 04/26/2018 04:15 AM, guangrong.xiao@gmail.com wrote: > > > > > From: Xiao Guangrong > > > > > > > > > > QEMU 2.13 enables strict check for compression & decompression to > > > > > make the migration more robuster, that depends on the source to fix > > > > > > > > s/robuster/robust/ > > > > > > > > > > Will fix, thank you for pointing it out. > > > > > > > > the internal design which triggers the unexpected error conditions > > > > > > > > 2.13 hasn't been released yet. Why do we need a knob to explicitly turn > > > > off strict checking? Can we not instead make 2.13 automatically smart > > > > enough to tell if the incoming stream is coming from an older qemu > > > > (which might fail if the strict checks are enabled) vs. a newer qemu > > > > (the sender gave us what we need to ensure the strict checks are > > > > worthwhile)? > > > > > > > > > > Really smart. > > > > > > How about introduce a new command, MIG_CMD_DECOMPRESS_ERR_CHECK, > > > the destination will do strict check if got this command (i.e, new > > > QEMU is running on the source), otherwise, turn the check off. > > > > Why not we just introduce a compat bit for that? I mean something > > like: 15c3850325 ("migration: move skip_section_footers", > > 2017-06-28). Then we turn that check bit off for <=2.12. > > > > Would that work? > > I am afraid it can not. :( > > The compat bit only impacts local behavior, however, in this case, we > need the source QEMU to tell the destination if it supports strict > error check. My understanding is that the new compat bit will only take effect when at destination. I'm not sure I'm thinking that correctly. I'll give some examples. When we migrate from <2.12 to 2.13, on 2.13 QEMU we'll possibly with (using q35 as example, always) "-M pc-q35-2.12" to make the migration work, so this will let the destination QEMU stop checking decompressing errors. IMHO that's what we want so it's fine (forward migration). When we migrate from 2.13 to <2.12, on 2.12 it'll always skip checking decompression errors, so it's fine too even if we don't send some compress-errored pages. Then, would this mean that the compat bit could work too just like this patch? AFAIU the compat bit idea is very similar to current patch, however we don't really need a new parameter to make things complicated, we just let old QEMUs behave differently and automatically, then user won't need to worry about manually specify that parameter. Thanks, -- Peter Xu From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:60016) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fDi3I-0001iI-B3 for qemu-devel@nongnu.org; Tue, 01 May 2018 23:03:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fDi3D-0003WP-Pj for qemu-devel@nongnu.org; Tue, 01 May 2018 23:03:32 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:43754 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fDi3D-0003Vm-E3 for qemu-devel@nongnu.org; Tue, 01 May 2018 23:03:27 -0400 Date: Wed, 2 May 2018 11:03:09 +0800 From: Peter Xu Message-ID: <20180502030309.GC25938@xz-mi> References: <20180426091519.26934-1-xiaoguangrong@tencent.com> <32eaad8e-35a0-5240-37a2-4242b7890ab9@redhat.com> <20180427093135.GC13269@xz-mi> <2f84ab90-2b9c-9888-e6e2-9114ae046078@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <2f84ab90-2b9c-9888-e6e2-9114ae046078@gmail.com> Subject: Re: [Qemu-devel] [PATCH] migration: introduce decompress-error-check List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Xiao Guangrong Cc: Eric Blake , pbonzini@redhat.com, mst@redhat.com, mtosatti@redhat.com, kvm@vger.kernel.org, Xiao Guangrong , qemu-devel@nongnu.org, dgilbert@redhat.com, wei.w.wang@intel.com, jiang.biao2@zte.com.cn On Fri, Apr 27, 2018 at 06:40:09PM +0800, Xiao Guangrong wrote: > > > On 04/27/2018 05:31 PM, Peter Xu wrote: > > On Fri, Apr 27, 2018 at 11:15:37AM +0800, Xiao Guangrong wrote: > > > > > > > > > On 04/26/2018 10:01 PM, Eric Blake wrote: > > > > On 04/26/2018 04:15 AM, guangrong.xiao@gmail.com wrote: > > > > > From: Xiao Guangrong > > > > > > > > > > QEMU 2.13 enables strict check for compression & decompression to > > > > > make the migration more robuster, that depends on the source to fix > > > > > > > > s/robuster/robust/ > > > > > > > > > > Will fix, thank you for pointing it out. > > > > > > > > the internal design which triggers the unexpected error conditions > > > > > > > > 2.13 hasn't been released yet. Why do we need a knob to explicitly turn > > > > off strict checking? Can we not instead make 2.13 automatically smart > > > > enough to tell if the incoming stream is coming from an older qemu > > > > (which might fail if the strict checks are enabled) vs. a newer qemu > > > > (the sender gave us what we need to ensure the strict checks are > > > > worthwhile)? > > > > > > > > > > Really smart. > > > > > > How about introduce a new command, MIG_CMD_DECOMPRESS_ERR_CHECK, > > > the destination will do strict check if got this command (i.e, new > > > QEMU is running on the source), otherwise, turn the check off. > > > > Why not we just introduce a compat bit for that? I mean something > > like: 15c3850325 ("migration: move skip_section_footers", > > 2017-06-28). Then we turn that check bit off for <=2.12. > > > > Would that work? > > I am afraid it can not. :( > > The compat bit only impacts local behavior, however, in this case, we > need the source QEMU to tell the destination if it supports strict > error check. My understanding is that the new compat bit will only take effect when at destination. I'm not sure I'm thinking that correctly. I'll give some examples. When we migrate from <2.12 to 2.13, on 2.13 QEMU we'll possibly with (using q35 as example, always) "-M pc-q35-2.12" to make the migration work, so this will let the destination QEMU stop checking decompressing errors. IMHO that's what we want so it's fine (forward migration). When we migrate from 2.13 to <2.12, on 2.12 it'll always skip checking decompression errors, so it's fine too even if we don't send some compress-errored pages. Then, would this mean that the compat bit could work too just like this patch? AFAIU the compat bit idea is very similar to current patch, however we don't really need a new parameter to make things complicated, we just let old QEMUs behave differently and automatically, then user won't need to worry about manually specify that parameter. Thanks, -- Peter Xu