Re: [Qemu-devel] [PATCH] intel-iommu: optimize nodmar memory regions

[Sergio Lopez]

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 <address@hidden>
> Signed-off-by: Peter Xu <address@hidden>
> ---
>
> 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.

Thanks!
Sergio.