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([2a01:e0a:280:24f0:3f78:514a:4f03:fdc0]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-46a3e6778f5sm4332561cf.28.2024.12.19.01.50.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 19 Dec 2024 01:50:50 -0800 (PST) Message-ID: <248fbb62-3433-4a38-b93d-afcf88205e3d@redhat.com> Date: Thu, 19 Dec 2024 10:50:47 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 24/24] vfio/migration: Multifd device state transfer support - send side To: Peter Xu , "Maciej S. Szmigiero" Cc: Avihai Horon , Alex Williamson , Fabiano Rosas , Eric Blake , Markus Armbruster , =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= , Joao Martins , qemu-devel@nongnu.org References: <4f5c33b97be09fcb4e1885073e31c5e930a39ad0.1731773021.git.maciej.szmigiero@oracle.com> <51279885-5229-4c5f-93af-d1214dd65f90@nvidia.com> <06360868-95e3-46e2-8960-51348025a1b7@maciej.szmigiero.name> <1ea676b5-c52a-4745-b5ce-f0376b1e6473@nvidia.com> <8f38a345-ad63-4168-907e-ac1cf736b2d1@maciej.szmigiero.name> Content-Language: en-US, fr From: =?UTF-8?Q?C=C3=A9dric_Le_Goater?= Autocrypt: addr=clg@redhat.com; keydata= xsFNBFu8o3UBEADP+oJVJaWm5vzZa/iLgpBAuzxSmNYhURZH+guITvSySk30YWfLYGBWQgeo 8NzNXBY3cH7JX3/a0jzmhDc0U61qFxVgrPqs1PQOjp7yRSFuDAnjtRqNvWkvlnRWLFq4+U5t yzYe4SFMjFb6Oc0xkQmaK2flmiJNnnxPttYwKBPd98WfXMmjwAv7QfwW+OL3VlTPADgzkcqj 53bfZ4VblAQrq6Ctbtu7JuUGAxSIL3XqeQlAwwLTfFGrmpY7MroE7n9Rl+hy/kuIrb/TO8n0 ZxYXvvhT7OmRKvbYuc5Jze6o7op/bJHlufY+AquYQ4dPxjPPVUT/DLiUYJ3oVBWFYNbzfOrV RxEwNuRbycttMiZWxgflsQoHF06q/2l4ttS3zsV4TDZudMq0TbCH/uJFPFsbHUN91qwwaN/+ gy1j7o6aWMz+Ib3O9dK2M/j/O/Ube95mdCqN4N/uSnDlca3YDEWrV9jO1mUS/ndOkjxa34ia 70FjwiSQAsyIwqbRO3CGmiOJqDa9qNvd2TJgAaS2WCw/TlBALjVQ7AyoPEoBPj31K74Wc4GS Rm+FSch32ei61yFu6ACdZ12i5Edt+To+hkElzjt6db/UgRUeKfzlMB7PodK7o8NBD8outJGS tsL2GRX24QvvBuusJdMiLGpNz3uqyqwzC5w0Fd34E6G94806fwARAQABzSJDw6lkcmljIExl IEdvYXRlciA8Y2xnQHJlZGhhdC5jb20+wsGRBBMBCAA7FiEEoPZlSPBIlev+awtgUaNDx8/7 7KEFAmTLlVECGwMFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgkQUaNDx8/77KG0eg// S0zIzTcxkrwJ/9XgdcvVTnXLVF9V4/tZPfB7sCp8rpDCEseU6O0TkOVFoGWM39sEMiQBSvyY lHrP7p7E/JYQNNLh441MfaX8RJ5Ul3btluLapm8oHp/vbHKV2IhLcpNCfAqaQKdfk8yazYhh EdxTBlzxPcu+78uE5fF4wusmtutK0JG0sAgq0mHFZX7qKG6LIbdLdaQalZ8CCFMKUhLptW71 xe+aNrn7hScBoOj2kTDRgf9CE7svmjGToJzUxgeh9mIkxAxTu7XU+8lmL28j2L5uNuDOq9vl hM30OT+pfHmyPLtLK8+GXfFDxjea5hZLF+2yolE/ATQFt9AmOmXC+YayrcO2ZvdnKExZS1o8 VUKpZgRnkwMUUReaF/mTauRQGLuS4lDcI4DrARPyLGNbvYlpmJWnGRWCDguQ/LBPpbG7djoy k3NlvoeA757c4DgCzggViqLm0Bae320qEc6z9o0X0ePqSU2f7vcuWN49Uhox5kM5L86DzjEQ RHXndoJkeL8LmHx8DM+kx4aZt0zVfCHwmKTkSTQoAQakLpLte7tWXIio9ZKhUGPv/eHxXEoS 0rOOAZ6np1U/xNR82QbF9qr9TrTVI3GtVe7Vxmff+qoSAxJiZQCo5kt0YlWwti2fFI4xvkOi V7lyhOA3+/3oRKpZYQ86Frlo61HU3r6d9wzOwU0EW7yjdQEQALyDNNMw/08/fsyWEWjfqVhW pOOrX2h+z4q0lOHkjxi/FRIRLfXeZjFfNQNLSoL8j1y2rQOs1j1g+NV3K5hrZYYcMs0xhmrZ KXAHjjDx7FW3sG3jcGjFW5Xk4olTrZwFsZVUcP8XZlArLmkAX3UyrrXEWPSBJCXxDIW1hzwp bV/nVbo/K9XBptT/wPd+RPiOTIIRptjypGY+S23HYBDND3mtfTz/uY0Jytaio9GETj+fFis6 TxFjjbZNUxKpwftu/4RimZ7qL+uM1rG1lLWc9SPtFxRQ8uLvLOUFB1AqHixBcx7LIXSKZEFU CSLB2AE4wXQkJbApye48qnZ09zc929df5gU6hjgqV9Gk1rIfHxvTsYltA1jWalySEScmr0iS YBZjw8Nbd7SxeomAxzBv2l1Fk8fPzR7M616dtb3Z3HLjyvwAwxtfGD7VnvINPbzyibbe9c6g LxYCr23c2Ry0UfFXh6UKD83d5ybqnXrEJ5n/t1+TLGCYGzF2erVYGkQrReJe8Mld3iGVldB7 JhuAU1+d88NS3aBpNF6TbGXqlXGF6Yua6n1cOY2Yb4lO/mDKgjXd3aviqlwVlodC8AwI0Sdu jWryzL5/AGEU2sIDQCHuv1QgzmKwhE58d475KdVX/3Vt5I9kTXpvEpfW18TjlFkdHGESM/Jx IqVsqvhAJkalABEBAAHCwV8EGAECAAkFAlu8o3UCGwwACgkQUaNDx8/77KEhwg//WqVopd5k 8hQb9VVdk6RQOCTfo6wHhEqgjbXQGlaxKHoXywEQBi8eULbeMQf5l4+tHJWBxswQ93IHBQjK yKyNr4FXseUI5O20XVNYDJZUrhA4yn0e/Af0IX25d94HXQ5sMTWr1qlSK6Zu79lbH3R57w9j hQm9emQEp785ui3A5U2Lqp6nWYWXz0eUZ0Tad2zC71Gg9VazU9MXyWn749s0nXbVLcLS0yop s302Gf3ZmtgfXTX/W+M25hiVRRKCH88yr6it+OMJBUndQVAA/fE9hYom6t/zqA248j0QAV/p LHH3hSirE1mv+7jpQnhMvatrwUpeXrOiEw1nHzWCqOJUZ4SY+HmGFW0YirWV2mYKoaGO2YBU wYF7O9TI3GEEgRMBIRT98fHa0NPwtlTktVISl73LpgVscdW8yg9Gc82oe8FzU1uHjU8b10lU XOMHpqDDEV9//r4ZhkKZ9C4O+YZcTFu+mvAY3GlqivBNkmYsHYSlFsbxc37E1HpTEaSWsGfA HQoPn9qrDJgsgcbBVc1gkUT6hnxShKPp4PlsZVMNjvPAnr5TEBgHkk54HQRhhwcYv1T2QumQ izDiU6iOrUzBThaMhZO3i927SG2DwWDVzZltKrCMD1aMPvb3NU8FOYRhNmIFR3fcalYr+9gD uVKe8BVz4atMOoktmt0GWTOC8P4= In-Reply-To: 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: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 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, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1.116, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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 12/16/24 18:33, Peter Xu wrote: > On Thu, Dec 12, 2024 at 11:53:05PM +0100, Maciej S. Szmigiero wrote: >> On 12.12.2024 15:54, Avihai Horon wrote: >>> >>> On 11/12/2024 1:06, Maciej S. Szmigiero wrote: >>>> External email: Use caution opening links or attachments >>>> >>>> >>>> On 9.12.2024 10:28, Avihai Horon wrote: >>>>> >>>>> On 17/11/2024 21:20, Maciej S. Szmigiero wrote: >>>>>> External email: Use caution opening links or attachments >>>>>> >>>>>> >>>>>> From: "Maciej S. Szmigiero" >>>>>> >>>>>> Implement the multifd device state transfer via additional per-device >>>>>> thread inside save_live_complete_precopy_thread handler. >>>>>> >>>>>> Switch between doing the data transfer in the new handler and doing it >>>>>> in the old save_state handler depending on the >>>>>> x-migration-multifd-transfer device property value. >>>>>> >>>>>> Signed-off-by: Maciej S. Szmigiero >>>>>> --- >>>>>>   hw/vfio/migration.c  | 155 +++++++++++++++++++++++++++++++++++++++++++ >>>>>>   hw/vfio/trace-events |   2 + >>>>>>   2 files changed, 157 insertions(+) >>>>>> >>>>>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c >>>>>> index b54879fe6209..8709672ada48 100644 >>>>>> --- a/hw/vfio/migration.c >>>>>> +++ b/hw/vfio/migration.c >>>>>> @@ -771,6 +771,24 @@ static int vfio_save_setup(QEMUFile *f, void *opaque, Error **errp) >>>>>>       uint64_t stop_copy_size = VFIO_MIG_DEFAULT_DATA_BUFFER_SIZE; >>>>>>       int ret; >>>>>> >>>>>> +    /* >>>>>> +     * Make a copy of this setting at the start in case it is changed >>>>>> +     * mid-migration. >>>>>> +     */ >>>>>> +    if (vbasedev->migration_multifd_transfer == ON_OFF_AUTO_AUTO) { >>>>>> +        migration->multifd_transfer = vfio_multifd_transfer_supported(); >>>>>> +    } else { >>>>>> +        migration->multifd_transfer = >>>>>> +            vbasedev->migration_multifd_transfer == ON_OFF_AUTO_ON; >>>>>> +    } >>>>>> + >>>>>> +    if (migration->multifd_transfer && !vfio_multifd_transfer_supported()) { >>>>>> +        error_setg(errp, >>>>>> +                   "%s: Multifd device transfer requested but unsupported in the current config", >>>>>> +                   vbasedev->name); >>>>>> +        return -EINVAL; >>>>>> +    } >>>>>> + >>>>>>       qemu_put_be64(f, VFIO_MIG_FLAG_DEV_SETUP_STATE); >>>>>> >>>>>>       vfio_query_stop_copy_size(vbasedev, &stop_copy_size); >>>>>> @@ -942,13 +960,32 @@ static int vfio_save_iterate(QEMUFile *f, void *opaque) >>>>>>       return !migration->precopy_init_size && !migration->precopy_dirty_size; >>>>>>   } >>>>>> >>>>>> +static void vfio_save_multifd_emit_dummy_eos(VFIODevice *vbasedev, QEMUFile *f) >>>>>> +{ >>>>>> +    VFIOMigration *migration = vbasedev->migration; >>>>>> + >>>>>> +    assert(migration->multifd_transfer); >>>>>> + >>>>>> +    /* >>>>>> +     * Emit dummy NOP data on the main migration channel since the actual >>>>>> +     * device state transfer is done via multifd channels. >>>>>> +     */ >>>>>> +    qemu_put_be64(f, VFIO_MIG_FLAG_END_OF_STATE); >>>>>> +} >>>>>> + >>>>>>   static int vfio_save_complete_precopy(QEMUFile *f, void *opaque) >>>>>>   { >>>>>>       VFIODevice *vbasedev = opaque; >>>>>> +    VFIOMigration *migration = vbasedev->migration; >>>>>>       ssize_t data_size; >>>>>>       int ret; >>>>>>       Error *local_err = NULL; >>>>>> >>>>>> +    if (migration->multifd_transfer) { >>>>>> +        vfio_save_multifd_emit_dummy_eos(vbasedev, f); >>>>>> +        return 0; >>>>>> +    } >>>>> >>>>> I wonder whether we should add a .save_live_use_thread SaveVMHandlers through which a device can indicate if it wants to save its data with the async or sync handler. >>>>> This will allow migration layer (i.e., qemu_savevm_state_complete_precopy_iterable) to know which handler to call instead of calling both of them and letting each device implicitly decide. >>>>> IMHO it will make the code clearer and will allow us to drop vfio_save_multifd_emit_dummy_eos(). >>>> >>>> I think that it's not worth adding a new SaveVMHandler just for this specific >>>> use case, considering that it's easy to handle it inside driver by emitting that >>>> FLAG_END_OF_STATE. >>>> >>>> Especially considering that for compatibility with other drivers that do not >>>> define that hypothetical new SaveVMHandler not having it defined would need to >>>> have the same effect as it always returning "false". >>> >>> We already have such handlers like .is_active, .has_postcopy and .is_active_iterate. >>> Since VFIO migration with multifd involves a lot of threads and convoluted code paths, I thought this could put some order (even if small) into things, especially if it allows us to avoid the vfio_save_multifd_emit_dummy_eos() which feels a bit hackish. >>> >>> But anyway, that's only my opinion, and I can understand why this could be seen as an overkill. >> >> @Cedric, @Peter: >> what's your opinion here? >> >> Is it better to add a new "flag" SaveVMHandler or keep handling >> the multifd/non-multifd transfer difference in the VFIO driver >> by emitting VFIO_MIG_FLAG_END_OF_STATE in >> vfio_save_complete_precopy() and vfio_save_state()? >> >> Note that this new "flag" SaveVMHandler would need to have >> semantics of disabling both save_live_complete_precopy and >> save_state handlers and enabling save_live_complete_precopy_thread >> instead. > > If it's about adding one more global vmstate hook (even if only used in > vfio), only to conditionally disable two other random vmstate hooks, then > it isn't very attractive idea to me indeed. We will need the 'multifd_transfer' VFIO field anyhow (not sure why it is not at the device level yet though). So I guess it is fine to keep it that way. However, I would rename vfio_save_multifd_emit_dummy_eos() to something more explicit like vfio_multifd_complete_precopy(). Thanks, C. > > PS: when I look at is_active (which is only used by two sites but needs to > be invoked in literally all the rest hooks, and I doubt whether it could > change during migration at all..), or has_postcopy (which is weird in > another way, e.g., should we simply forbid pmem+postcopy setup upfront?), I > doubt whether they were the best solution for the problems.. but that's > separate questions to ask. > > Thanks, >