On 13/03/19 12:45, Sergio Lopez wrote: > > Peter Xu writes: > >> Previously we have per-device system memory aliases when DMAR is >> disabled by the system. It will slow the system down if there are >> lots of devices especially when DMAR is disabled, because each of the >> aliased system address space will contain O(N) slots, and rendering >> such N address spaces will be O(N^2) complexity. >> >> This patch introduces a shared nodmar memory region and for each >> device we only create an alias to the shared memory region. With the >> aliasing, QEMU memory core API will be able to detect when devices are >> sharing the same address space (which is the nodmar address space) >> when rendering the FlatViews and the total number of FlatViews can be >> dramatically reduced when there are a lot of devices. >> >> Suggested-by: Paolo Bonzini <pbonz...@redhat.com> >> Signed-off-by: Peter Xu <pet...@redhat.com> >> --- >> >> Hi, Sergio, >> >> This patch implements the optimization that Paolo proposed in the >> other thread. Would you please try this patch to see whether it could >> help for your case? Thanks, > > Hi, > > I've just gave a try and it fixes the issue here. The number of > FlatViews goes down from 119 to 4, and the initialization time for PCI > devices on the Guest is back to normal levels.
You must be using "iommu=pt" then. Can you also test performance without it? It should be fine even if the number of FlatViews goes back to 119. Paolo
