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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?nTswAtVj1EuA+20PuD7D9pHwczg7ZhlFPbMmS1hHcl7oHplSAwfB3/wbhUwH?= =?us-ascii?Q?znnyfJhJem0ei+VmkR4d38hKoiFKRiWO/g6ZEspDOV22GMmgaVoe9bYCTGre?= =?us-ascii?Q?OMMEFTBYarArWb6KqRxh4upbVNpGW32HNxBBBX0hh55XkSEdK5iV02R2N9BW?= =?us-ascii?Q?01J6B+sJS13cXKVgryhGvffOF1etswLLVZ/J20zIBJiLUR5iqIMp4XMiUsZ/?= =?us-ascii?Q?JsSzVoKhyYMzFvGJPL8Z105N04s5Aj6ERr62VeLa6saZkpXAE7Un6UVKl+zI?= =?us-ascii?Q?OolfFiFzc+9igTFcn2tXEpXW5XR/rN2HFCNAYT7J70yjUSJE+VufcEZ1n6HQ?= =?us-ascii?Q?UPwNTQJlEbR8InJfewPDHCJ6nEd8CXzrQNIAo+uK+1rJGEfFKZ0Rh7tgidK4?= =?us-ascii?Q?WSiY0lvHFuUulQdnoUbMs5JMJdStssngeU7xWtCsjDr9MP57DSzCHGw+Sdyh?= =?us-ascii?Q?ydiN1CpJBk68FmdYOukm3f3ane02HsYH3bPmVYQBV5dKgjpPuMUdnC4lwKma?= =?us-ascii?Q?6zVqOSqIfv8KkSCahzLlGdb3vdIhVds2ApCmxulEud57IsRYxRdechZWXl8s?= =?us-ascii?Q?4EPn/3RhvbSmiyd8i3Z+a8z947PoT3cYuAZOmHo7uuQu/js8dDqiQOxWgW7W?= =?us-ascii?Q?Af7nSUt+b1qqnQO7us8ihd/5PSg8Su4I2g+uNZGGKk547kxOQ7MGUOewxFwI?= =?us-ascii?Q?SAHEAXGkyYy1L9iSBsbvdXZrXhSgXXMhz7iKEgzle87Ce7Ly+cY0NtUwAeP0?= =?us-ascii?Q?th2wvioYcRlTfllegMX05Y9znUH8LHqkfVD7+vXNgMNNjH7lyjnwYjyoUqMY?= =?us-ascii?Q?etlbJBtPOsGq8yAylZ9my+ua/ggD0Fqmes+WOa78iXhUF+2SRQtW0qDrnVpk?= =?us-ascii?Q?0AH/iJrryZZyIy6x+hISUZuLe/CACgohYIRCr9Z7WkIgCnIY+2EyKV95hyNy?= =?us-ascii?Q?HgAn+ArGbukBMofKTgfRdOGJubSJ7l6isFsfjOusMK08JyhktxSLnUBepBcH?= =?us-ascii?Q?jYP6ZJHQuqLnHyFXHRnXNoUEu+eD2QGxYG/YQxRi3yg+aecq19ne/i7gQx/y?= =?us-ascii?Q?3+jjWahIJkWsILEiEcuHKR/vO5UjqpYkho28XfZlQEwIMDt3p1NxbmGxde0R?= =?us-ascii?Q?AzvoGGnBADsM62tGuT8JmFjTuRmRXovGkYAldPR2Ig9nCIxmZ/NgyXmBeO8b?= =?us-ascii?Q?EL94ndQEyLspUfLMKJgkzurdfwnRO8slldHWAih/v/0sjLe3AGI3zsjoMR+h?= =?us-ascii?Q?zEMbsESqa4MU0n7XC3UwfrjeHj6NknD92zygltyyuNDm4Mc5R13M9biEul3H?= =?us-ascii?Q?sOIO8k5WuFjSFocktRJOtswTw0uTIG2n4zPWxE0BLZbBH76lQmPP2/4JRt+3?= =?us-ascii?Q?XV+0qDmVgYSN6OmofYS496SnHz9zu0vHU8xby76ropJwXGiP0iLvK8lQideN?= =?us-ascii?Q?X31edr028e3WUcVlgy/be7bTfAqJj8CrYXLxA8Rhplcw251+9LcFPbGXxjRP?= =?us-ascii?Q?euBDcKRDiIsCwUZn/cOqzLcHKqDY08Fs5YNpJSOPNnkxSw5fokRGKrTEqkNH?= =?us-ascii?Q?fHs6Sd7movOxR6XrttgvALLgWvy7MggDYehokvmv?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: fe9f3697-ac8a-4f13-cf47-08ddb4f3e0ad X-MS-Exchange-CrossTenant-AuthSource: CH3PR12MB8659.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Jun 2025 20:56:10.1371 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: mcae2iAPrUwuODNztVwZ1In9tNDQUC9mIF+5eJANs91YM88M2l8nWFsl+HzFAtrA X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY5PR12MB6083 On Thu, Jun 26, 2025 at 01:26:59PM -0600, Alex Williamson wrote: > On Thu, 26 Jun 2025 18:04:21 +0000 > Aaron Lewis wrote: > > > This series is being sent as an RFC to help brainstorm the best way to > > fix a latency issue it uncovers. > > > > The crux of the issue is that when initializing multiple VFs from the > > same PF the devices are reset serially rather than in parallel > > regardless if they are initialized from different threads. That happens > > because a shared lock is acquired when vfio_df_ioctl_bind_iommufd() is > > called, then a FLR (function level reset) is done which takes 100ms to > > complete. That in combination with trying to initialize many devices at > > the same time results in a lot of wasted time. > > > > While the PCI spec does specify that a FLR requires 100ms to ensure it > > has time to complete, I don't see anything indicating that other VFs > > can't be reset at the same time. > > > > A couple of ideas on how to approach a fix are: > > > > 1. See if the lock preventing the second thread from making forward > > progress can be sharded to only include the VF it protects. > > I think we're talking about the dev_set mutex here, right? I think this > is just an oversight. The original lock that dev_set replaced was > devised to manage the set of devices affected by the same bus or slot > reset. I believe we've held the same semantics though and VFs just > happen to fall through to the default of a bus-based dev_set. > Obviously we cannot do a bus or slot reset of a VF, we only have FLR, > and it especially doesn't make sense that VFs on the same "bus" from > different PFs share this mutex. It certainly could be.. But I am feeling a bit wary and would want to check this carefully. We ended up using the devset for more things - need to check where everything ended up. Off hand I don't recall any reason why the VF should be part of the dev set.. > diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c > index 6328c3a05bcd..261a6dc5a5fc 100644 > --- a/drivers/vfio/pci/vfio_pci_core.c > +++ b/drivers/vfio/pci/vfio_pci_core.c > @@ -2149,7 +2149,7 @@ int vfio_pci_core_register_device(struct vfio_pci_core_device *vdev) > return -EBUSY; > } > > - if (pci_is_root_bus(pdev->bus)) { > + if (pci_is_root_bus(pdev->bus) || pdev->is_virtfn) { > ret = vfio_assign_device_set(&vdev->vdev, vdev); > } else if (!pci_probe_reset_slot(pdev->slot)) { > ret = vfio_assign_device_set(&vdev->vdev, pdev->slot); > > Does that allow fully parallelized resets? I forget all the details but if we are sure the reset of a VF is only the VF then that does seem like the right direction Jason