On 07-09-2026 11:17, Naman Jain wrote: > On Hyper-V guests each virtual PCI bus is enumerated by its own > hv_pci_probe() call. The probe performs several synchronous host > request/response exchanges while negotiating the protocol, querying bus > relations, entering D0, and reporting allocated resources. These waits > are latency-bound rather than CPU-bound. > > hv_pci registers as an ordinary VMBus driver, so driver_register() walks > matching vPCI buses and probes them sequentially while the driver's > initcall runs. On guests that expose several devices, each through its > own vPCI bus, this serialization adds the host round-trip latencies to > device initialization. > > Each bus is described by its own struct hv_pcibus_device, so > independent buses can be probed concurrently. Request asynchronous > probing via PROBE_PREFER_ASYNCHRONOUS, causing the driver core to > schedule matching buses for asynchronous probe work. > > On an Azure Standard_L32s_v3 guest with five vPCI targets (four NVMe > controllers and one Mellanox VF), Linux 7.2.3 was tested with one warm-up > and three measured boots per variant. The median interval from the first > hv_pci_probe() entry to the last return decreased from 2847.968 ms to > 2786.709 ms, a 61.259 ms (2.15%) improvement. > > Co-developed-by: Dexuan Cui <[email protected]> > Signed-off-by: Dexuan Cui <[email protected]> > Signed-off-by: Naman Jain <[email protected]> > --- > > Previous discussion around this change: > https://lore.kernel.org/all/[email protected]/ > > Skipping removal of pci_rescan_remove_lock, due to possible > synchronization problems associated with this lock removal. Also, with > my current setup, I was not able to see much improvements with this > change, so keeping it for later. Asynchronous probing change is not > dependent on this. > > --- > drivers/pci/controller/pci-hyperv.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/pci/controller/pci-hyperv.c > b/drivers/pci/controller/pci-hyperv.c > index 89816a2bd7cd3..056d379b3cee4 100644 > --- a/drivers/pci/controller/pci-hyperv.c > +++ b/drivers/pci/controller/pci-hyperv.c > @@ -4155,6 +4155,9 @@ static struct hv_driver hv_pci_drv = { > .remove = hv_pci_remove, > .suspend = hv_pci_suspend, > .resume = hv_pci_resume, > + .driver = { > + .probe_type = PROBE_PREFER_ASYNCHRONOUS, > + }, > }; > > static void __exit exit_hv_pci_drv(void) LGTM. Reviewed-by: Sahil Chandna <[email protected]>
Regards, Sahil
