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Tsirkin" To: Peter Xu Cc: Prasad Pandit , qemu-devel@nongnu.org, Fabiano Rosas , Jason Wang , mcoqueli@redhat.com, Prasad Pandit Subject: Re: [PATCH 0/2] Postcopy migration and vhost-user errors Message-ID: <20240717045335-mutt-send-email-mst@kernel.org> References: <20240711131424.181615-1-ppandit@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Received-SPF: pass client-ip=170.10.133.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, DKIM_INVALID=0.1, DKIM_SIGNED=0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Jul 16, 2024 at 06:02:50PM -0400, Peter Xu wrote: > On Tue, Jul 16, 2024 at 03:44:54PM +0530, Prasad Pandit wrote: > > Hello Peter, > > > > On Mon, 15 Jul 2024 at 19:10, Peter Xu wrote: > > > IMHO it's better we debug and fix all the issues before merging this one, > > > otherwise we may overlook something. > > > > * Well we don't know where the issue is, not sure where the fix may go > > in, ex. if the issue turns out to be how virsh(1) invokes > > migrate-postcopy, fix may go in virsh(1). Patches in this series > > anyway don't help to fix the migration convergence issue, so they > > could be reviewed independently I guess. > > I still think we should find a complete solution before merging anything, > because I'm not 100% confident the issue to be further investigated is > irrelevant to this patch. > > No strong opinions, I'll leave that to Michael to decide. > > > > > > You could pass over the patch to whoever going to debug this, so it will be included in the whole set to be > > > posted when the bug is completely fixed. > > > > * Yes, this patch series is linked there. > > > > > The protocol should have no restriction on the thread model of a front-end. > > > It only describes the wire protocol. > > > > > > IIUC the protocol was designed to be serialized by nature (where there's no > > > request ID, so we can't match reply to any of the previous response), then > > > the front-end can manage the threads well to serialize all the requests, > > > like using this rwlock. > > > > * I see, okay. The simple protocol definition seems to indicate that > > it is meant for one front-end/back-end pair. If we are dividing the > > front-end across multiple threads, maybe we need a document to > > describe those threads and how they work, at least for the QEMU > > (front-end) side. Because the back-end could be a non-QEMU process, we > > can not do much there. (just thinking) > > IMHO that's not part of the protocol but impl details, so the current doc > looks all fine to me. > > Thanks, > > -- > Peter Xu I just want to understand how we managed to have two threads talking in parallel. BQL is normally enough, which path manages to invoke vhost-user with BQL not taken? Just check BQL taken on each vhost user invocation and you will figure it out. -- MST