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Tue, 7 Apr 2026 15:48:08 +0000 (UTC) Received: from localhost (unknown [10.44.34.43]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 84AD8180035F; Tue, 7 Apr 2026 15:48:05 +0000 (UTC) Date: Tue, 7 Apr 2026 11:48:03 -0400 From: Stefan Hajnoczi To: Alexander Mikhalitsyn Cc: qemu-devel@nongnu.org, Peter Xu , Fabiano Rosas , Jesper Devantier , Klaus Jensen , =?iso-8859-1?Q?St=E9phane?= Graber , qemu-block@nongnu.org, Hanna Reitz , Paolo Bonzini , Keith Busch , Fam Zheng , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , Zhao Liu , Kevin Wolf , Alexander Mikhalitsyn Subject: Re: [PATCH v5 7/8] hw/nvme: add basic live migration support Message-ID: <20260407154803.GB238768@fedora> References: <20260317102708.126725-1-alexander@mihalicyn.com> <20260317102708.126725-8-alexander@mihalicyn.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="sKp2MTVxKjtu18Kf" Content-Disposition: inline In-Reply-To: <20260317102708.126725-8-alexander@mihalicyn.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.129.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -25 X-Spam_score: -2.6 X-Spam_bar: -- X-Spam_report: (-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.54, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development 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 --sKp2MTVxKjtu18Kf Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Mar 17, 2026 at 11:27:07AM +0100, Alexander Mikhalitsyn wrote: > + /* wait when all in-flight IO requests (except NVME_ADM_CMD_ASYNC_EV_REQ) are processed */ > + for (i = 0; i < n->num_queues; i++) { > + NvmeRequest *req; > + NvmeSQueue *sq = n->sq[i]; > + > + if (!sq) > + continue; > + > + trace_pci_nvme_pre_save_sq_out_req_drain_wait(n, i, sq->head, sq->tail, sq->size); > + > +wait_out_reqs: > + QTAILQ_FOREACH(req, &sq->out_req_list, entry) { > + if (req->cmd.opcode != NVME_ADM_CMD_ASYNC_EV_REQ) { > + cpu_relax(); > + goto wait_out_reqs; > + } > + } > + > + trace_pci_nvme_pre_save_sq_out_req_drain_wait_end(n, i, sq->head, sq->tail); > + } Emulated storage controllers usually do not drain requests themselves. They rely on core migration code (e.g. migration_completion_precopy()) to stop vCPUs and call bdrv_drain_all_begin/end() to quiesce I/O. Why does NVMe busy wait for requests here? --sKp2MTVxKjtu18Kf Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQEzBAEBCgAdFiEEhpWov9P5fNqsNXdanKSrs4Grc8gFAmnVJzMACgkQnKSrs4Gr c8h/mQf+MW6VlcPNfiPB2YtWOoWy4hJa5e9Dv9K7z57ODtvGFbzzNgPmgypI9bKy ALAKZ3DcWfHIrCaCairw5A+8qEWNPDS5uW+I44AcNW3jgxtoKo3+SznL+2IHDLCl J8Won+bZsNn/Vio6csVDLNqunfOB2s1rk05o9b8UgeFKx5R8dCjGV33L7QuTPebm 0+jUChntpmLEt+Ux+NPK46P1x+pgXmvRoJSQgK3D2IgUny9EL+g0UvAF/OfH8W2A Vzb5ULYp66XkoJwq9d8V4Oyxiwit4xlfZMlw9KAR41e+pDiSmOnODHg/BrEe9P/b qlrNlWgtqYuyJKjRedc8jrMNqMsdgw== =eUr+ -----END PGP SIGNATURE----- --sKp2MTVxKjtu18Kf--