On Wed, Feb 28, 2018 at 01:45:54PM -0700, Alex Williamson wrote: > The NVIDIA BAR0 quirks virtualize the PCI config space mirrors found > in device MMIO space. Normally PCI config space is considered a slow > path and further optimization is unnecessary, however NVIDIA uses a > register here to enable the MSI interrupt to re-trigger. Exiting to > QEMU for this MSI-ACK handling can therefore rate limit our interrupt > handling. Fortunately the MSI-ACK write is easily detected since the > quirk MemoryRegion otherwise has very few accesses, so simply looking > for consecutive writes with the same data is sufficient, in this case > 10 consecutive writes with the same data and size is arbitrarily > chosen. We configure the KVM ioeventfd with data match, so there's > no risk of triggering for the wrong data or size, but we do risk that > pathological driver behavior might consume all of QEMU's file > descriptors, so we cap ourselves to 10 ioeventfds for this purpose. > > In support of the above, generic ioeventfd infrastructure is added > for vfio quirks. This automatically initializes an ioeventfd list > per quirk, disables and frees ioeventfds on exit, and allows > ioeventfds marked as dynamic to be dropped on device reset. The > rationale for this latter feature is that useful ioeventfds may > depend on specific driver behavior and since we necessarily place a > cap on our use of ioeventfds, a machine reset is a reasonable point > at which to assume a new driver and re-profile. > > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx> I don't know when will there be non-dynamic vfio-ioeventfds, but it looks fine at least to me even if all of them are dynamic now: Reviewed-by: Peter Xu <peterx@xxxxxxxxxx> -- Peter Xu
