Re: [PATCH] vfio/pci: Separate SR-IOV VF dev_set

[Yi Liu <yi.l.liu@intel.com>]

On 2025/6/27 06:56, Alex Williamson wrote:
> In the below noted Fixes commit we introduced a reflck mutex to allow
> better scaling between devices for open and close.  The reflck was
> based on the hot reset granularity, device level for root bus devices
> which cannot support hot reset or bus/slot reset otherwise.  Overlooked
> in this were SR-IOV VFs, where there's also no bus reset option, but
> the default for a non-root-bus, non-slot-based device is bus level
> reflck granularity.
> 
> The reflck mutex has since become the dev_set mutex and is our defacto
> serialization for various operations and ioctls.  It still seems to be
> the case though that sets of vfio-pci devices really only need

a nit: not sure if mentioning 2cd8b14aaa66 which convers reflck to dev_set
mutex is helpful. Perhaps, it's welcomed by people working on backporting. :)

> serialization relative to hot resets affecting the entire set, which
> is not relevant to SR-IOV VFs.  As described in the Closes link below,
> this serialization contributes to startup latency when multiple VFs
> sharing the same "bus" are opened concurrently.
> 
> Mark the device itself as the basis of the dev_set for SR-IOV VFs.
> 
> Reported-by: Aaron Lewis <aaronlewis@google.com>
> Closes: https://lore.kernel.org/all/20250626180424.632628-1-aaronlewis@google.com
> Tested-by: Aaron Lewis <aaronlewis@google.com>
> Fixes: e309df5b0c9e ("vfio/pci: Parallelize device open and release")
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> ---
>   drivers/vfio/pci/vfio_pci_core.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Yi Liu <yi.l.liu@intel.com>

Regards,
Yi Liu