On Mon, May 02, 2022 at 12:42:55AM -0700, Dexuan Cui wrote: > Currently when the pci-hyperv driver finishes probing and initializing the > PCI device, it sets the PCI_COMMAND_MEMORY bit; later when the PCI device > is registered to the core PCI subsystem, the core PCI driver's BAR detection > and initialization code toggles the bit multiple times, and each toggling of > the bit causes the hypervisor to unmap/map the virtual BARs from/to the > physical BARs, which can be slow if the BAR sizes are huge, e.g., a Linux VM > with 14 GPU devices has to spend more than 3 minutes on BAR detection and > initialization, causing a long boot time. > > Reduce the boot time by not setting the PCI_COMMAND_MEMORY bit when we > register the PCI device (there is no need to have it set in the first place). > The bit stays off till the PCI device driver calls pci_enable_device(). > With this change, the boot time of such a 14-GPU VM is reduced by almost > 3 minutes. > > Link: https://lore.kernel.org/lkml/20220419220007.26550-1-decui@xxxxxxxxxxxxx/ > Tested-by: Boqun Feng (Microsoft) <boqun.feng@xxxxxxxxx> > Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx> > Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx> > Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> > Cc: Jake Oshins <jakeo@xxxxxxxxxxxxx> Applied to hyperv-next. Thanks.
