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([2a01:e0a:280:24f0:9db0:474c:ff43:9f5c]) by smtp.gmail.com with ESMTPSA id v5-20020a1cf705000000b003f4e3ed98ffsm12083071wmh.35.2023.05.23.08.09.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 23 May 2023 08:09:03 -0700 (PDT) Message-ID: Date: Tue, 23 May 2023 17:09:01 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [PATCH v3 7/7] vfio/migration: Add support for switchover ack capability Content-Language: en-US To: Avihai Horon , qemu-devel@nongnu.org Cc: Alex Williamson , Eduardo Habkost , Marcel Apfelbaum , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Yanan Wang , Juan Quintela , Peter Xu , Leonardo Bras , Eric Blake , Markus Armbruster , Thomas Huth , Laurent Vivier , Paolo Bonzini , Yishai Hadas , Jason Gunthorpe , Maor Gottlieb , Kirti Wankhede , Tarun Gupta , Joao Martins References: <20230521151808.24804-1-avihaih@nvidia.com> <20230521151808.24804-8-avihaih@nvidia.com> From: =?UTF-8?Q?C=c3=a9dric_Le_Goater?= In-Reply-To: <20230521151808.24804-8-avihaih@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=clg@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.089, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, T_SCC_BODY_TEXT_LINE=-0.01, T_SPF_TEMPERROR=0.01 autolearn=ham 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 5/21/23 17:18, Avihai Horon wrote: > Loading of a VFIO device's data can take a substantial amount of time as > the device may need to allocate resources, prepare internal data > structures, etc. This can increase migration downtime, especially for > VFIO devices with a lot of resources. > > To solve this, VFIO migration uAPI defines "initial bytes" as part of > its precopy data stream. Initial bytes can be used in various ways to > improve VFIO migration performance. For example, it can be used to > transfer device metadata to pre-allocate resources in the destination. > However, for this to work we need to make sure that all initial bytes > are sent and loaded in the destination before the source VM is stopped. > > Use migration switchover ack capability to make sure a VFIO device's > initial bytes are sent and loaded in the destination before the source > stops the VM and attempts to complete the migration. > This can significantly reduce migration downtime for some devices. > > As precopy support and precopy initial bytes support come together in > VFIO migration, use x-allow-pre-copy device property to control usage of > this feature as well. > > Signed-off-by: Avihai Horon Reviewed-by: Cédric Le Goater > --- > docs/devel/vfio-migration.rst | 10 +++++++++ > include/hw/vfio/vfio-common.h | 2 ++ > hw/vfio/migration.c | 42 ++++++++++++++++++++++++++++++++++- > 3 files changed, 53 insertions(+), 1 deletion(-) > > diff --git a/docs/devel/vfio-migration.rst b/docs/devel/vfio-migration.rst > index e896b2a673..e75793b76a 100644 > --- a/docs/devel/vfio-migration.rst > +++ b/docs/devel/vfio-migration.rst > @@ -16,6 +16,13 @@ helps to reduce the total downtime of the VM. VFIO devices opt-in to pre-copy > support by reporting the VFIO_MIGRATION_PRE_COPY flag in the > VFIO_DEVICE_FEATURE_MIGRATION ioctl. > > +When pre-copy is supported, it's possible to further reduce downtime by > +enabling "switchover-ack" migration capability. > +VFIO migration uAPI defines "initial bytes" as part of its pre-copy data stream > +and recommends that the initial bytes are sent and loaded in the destination > +before stopping the source VM. Enabling this migration capability will > +guarantee that and thus, can potentially reduce downtime even further. > + > Note that currently VFIO migration is supported only for a single device. This > is due to VFIO migration's lack of P2P support. However, P2P support is planned > to be added later on. > @@ -45,6 +52,9 @@ VFIO implements the device hooks for the iterative approach as follows: > * A ``save_live_iterate`` function that reads the VFIO device's data from the > vendor driver during iterative pre-copy phase. > > +* A ``switchover_ack_needed`` function that checks if the VFIO device uses > + "switchover-ack" migration capability when this capability is enabled. > + > * A ``save_state`` function to save the device config space if it is present. > > * A ``save_live_complete_precopy`` function that sets the VFIO device in > diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h > index 5ce7a01d56..b4a7eb0f9a 100644 > --- a/include/hw/vfio/vfio-common.h > +++ b/include/hw/vfio/vfio-common.h > @@ -69,6 +69,8 @@ typedef struct VFIOMigration { > uint64_t precopy_init_size; > uint64_t precopy_dirty_size; > uint64_t mig_flags; > + bool switchover_ack_needed; > + bool initial_data_sent; > } VFIOMigration; > > typedef struct VFIOAddressSpace { > diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c > index 418efed019..09c669c1d8 100644 > --- a/hw/vfio/migration.c > +++ b/hw/vfio/migration.c > @@ -18,6 +18,7 @@ > #include "sysemu/runstate.h" > #include "hw/vfio/vfio-common.h" > #include "migration/migration.h" > +#include "migration/savevm.h" > #include "migration/vmstate.h" > #include "migration/qemu-file.h" > #include "migration/register.h" > @@ -45,6 +46,7 @@ > #define VFIO_MIG_FLAG_DEV_CONFIG_STATE (0xffffffffef100002ULL) > #define VFIO_MIG_FLAG_DEV_SETUP_STATE (0xffffffffef100003ULL) > #define VFIO_MIG_FLAG_DEV_DATA_STATE (0xffffffffef100004ULL) > +#define VFIO_MIG_FLAG_DEV_INIT_DATA_SENT (0xffffffffef100005ULL) > > /* > * This is an arbitrary size based on migration of mlx5 devices, where typically > @@ -380,6 +382,8 @@ static void vfio_save_cleanup(void *opaque) > > g_free(migration->data_buffer); > migration->data_buffer = NULL; > + migration->switchover_ack_needed = false; > + migration->initial_data_sent = false; > vfio_migration_cleanup(vbasedev); > trace_vfio_save_cleanup(vbasedev->name); > } > @@ -455,10 +459,17 @@ static int vfio_save_iterate(QEMUFile *f, void *opaque) > if (data_size < 0) { > return data_size; > } > - qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE); > > vfio_update_estimated_pending_data(migration, data_size); > > + if (migration->switchover_ack_needed && !migration->precopy_init_size && > + !migration->initial_data_sent) { > + qemu_put_be64(f, VFIO_MIG_FLAG_DEV_INIT_DATA_SENT); > + migration->initial_data_sent = true; > + } else { > + qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE); > + } > + > trace_vfio_save_iterate(vbasedev->name); > > /* > @@ -576,6 +587,24 @@ static int vfio_load_state(QEMUFile *f, void *opaque, int version_id) > } > break; > } > + case VFIO_MIG_FLAG_DEV_INIT_DATA_SENT: > + { > + if (!vbasedev->migration->switchover_ack_needed) { > + error_report("%s: Received INIT_DATA_SENT but switchover ack " > + "is not needed", > + vbasedev->name); This extra line could be avoided. This is minor. > + return -EINVAL; > + } > + > + ret = qemu_loadvm_approve_switchover(); > + if (ret) { > + error_report( > + "%s: qemu_loadvm_approve_switchover failed, err=%d (%s)", > + vbasedev->name, ret, strerror(-ret)); > + } > + > + return ret; > + } > default: > error_report("%s: Unknown tag 0x%"PRIx64, vbasedev->name, data); > return -EINVAL; > @@ -590,6 +619,16 @@ static int vfio_load_state(QEMUFile *f, void *opaque, int version_id) > return ret; > } > > +static bool vfio_switchover_ack_needed(void *opaque) > +{ > + VFIODevice *vbasedev = opaque; > + VFIOMigration *migration = vbasedev->migration; > + > + migration->switchover_ack_needed = vfio_precopy_supported(vbasedev); > + > + return migration->switchover_ack_needed; > +} > + > static const SaveVMHandlers savevm_vfio_handlers = { > .save_setup = vfio_save_setup, > .save_cleanup = vfio_save_cleanup, > @@ -602,6 +641,7 @@ static const SaveVMHandlers savevm_vfio_handlers = { > .load_setup = vfio_load_setup, > .load_cleanup = vfio_load_cleanup, > .load_state = vfio_load_state, > + .switchover_ack_needed = vfio_switchover_ack_needed, > }; > > /* ---------------------------------------------------------------------- */