On Thu, Sep 17, 2026 at 11:01:03AM +0530, Sahil Chandna wrote: > 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]>
Applied. Thanks.
