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Szmigiero" Cc: Alex Williamson , Fabiano Rosas , Peter Xu , =?UTF-8?Q?C=C3=A9dric_Le_Goater?= , Eric Blake , Markus Armbruster , =?UTF-8?Q?Daniel_P_=2E_Berrang=C3=A9?= , Joao Martins , qemu-devel@nongnu.org References: <3c43bf662842e579c0009dfc5135024e45166987.1724701542.git.maciej.szmigiero@oracle.com> <8ec6abeb-25ee-417e-9f3f-d0f27ec4f370@nvidia.com> <57835a25-10f9-4484-bd20-9e4e90a590e9@maciej.szmigiero.name> Content-Language: en-US From: Avihai Horon In-Reply-To: <57835a25-10f9-4484-bd20-9e4e90a590e9@maciej.szmigiero.name> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: FR4P281CA0333.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:ea::8) To DM6PR12MB5549.namprd12.prod.outlook.com (2603:10b6:5:209::13) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6PR12MB5549:EE_|SN7PR12MB6862:EE_ X-MS-Office365-Filtering-Correlation-Id: ab54caf9-7e76-4cd9-05c5-08dcd2711e28 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014; 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envelope-from=avihaih@nvidia.com; helo=NAM10-MW2-obe.outbound.protection.outlook.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=-0.144, 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=-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=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 09/09/2024 21:04, Maciej S. Szmigiero wrote: > External email: Use caution opening links or attachments > > > On 5.09.2024 15:08, Avihai Horon wrote: >> Hi Maciej, >> >> On 27/08/2024 20:54, Maciej S. Szmigiero wrote: >>> External email: Use caution opening links or attachments >>> >>> >>> From: "Maciej S. Szmigiero" >>> >>> This way both the start and end points of migrating a particular VFIO >>> device are known. >>> >>> Add also a vfio_save_iterate_empty_hit trace event so it is known when >>> there's no more data to send for that device. >> >> Out of curiosity, what are these traces used for? > > Just for benchmarking, collecting these data makes it easier to > reason where possible bottlenecks may be. > >>> >>> Signed-off-by: Maciej S. Szmigiero >>> --- >>>   hw/vfio/migration.c           | 13 +++++++++++++ >>>   hw/vfio/trace-events          |  3 +++ >>>   include/hw/vfio/vfio-common.h |  3 +++ >>>   3 files changed, 19 insertions(+) >>> >>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c >>> index 262d42a46e58..24679d8c5034 100644 >>> --- a/hw/vfio/migration.c >>> +++ b/hw/vfio/migration.c >>> @@ -472,6 +472,9 @@ static int vfio_save_setup(QEMUFile *f, void >>> *opaque, Error **errp) >>>           return -ENOMEM; >>>       } >>> >>> +    migration->save_iterate_run = false; >>> +    migration->save_iterate_empty_hit = false; >>> + >>>       if (vfio_precopy_supported(vbasedev)) { >>>           switch (migration->device_state) { >>>           case VFIO_DEVICE_STATE_RUNNING: >>> @@ -605,9 +608,17 @@ static int vfio_save_iterate(QEMUFile *f, void >>> *opaque) >>>       VFIOMigration *migration = vbasedev->migration; >>>       ssize_t data_size; >>> >>> +    if (!migration->save_iterate_run) { >>> +        trace_vfio_save_iterate_started(vbasedev->name); >>> +        migration->save_iterate_run = true; >> >> Maybe rename save_iterate_run to save_iterate_started so it's aligned >> with trace_vfio_save_iterate_started and >> trace_vfio_save_complete_precopy_started? > > Will do. > >>> +    } >>> + >>>       data_size = vfio_save_block(f, migration); >>>       if (data_size < 0) { >>>           return data_size; >>> +    } else if (data_size == 0 && !migration->save_iterate_empty_hit) { >>> +        trace_vfio_save_iterate_empty_hit(vbasedev->name); >>> +        migration->save_iterate_empty_hit = true; >> >> During precopy we could hit empty multiple times. Any reason why only >> the first time should be traced? > > This trace point is supposed to indicate whether the device state > transfer during the time the VM was still running likely has > exhausted the amount of data that can be transferred during > that phase. > > In other words, the stopped-time device state transfer likely > only had to transfer the data which the device does not support > transferring during the live VM phase (with just a small possible > residual accrued since that trace point was hit). > > If that trace point was hit then delaying the switch over point > further likely wouldn't help the device transfer less data during > the downtime. Ah, I see. Can we achieve the same goal by using trace_vfio_state_pending_exact() instead? Thanks.