Re: [RFC PATCH V3 0/5] Hi:

Michael S. Tsirkin
2019-01-04T21:41:24Z

On Sat, Dec 29, 2018 at 08:46:51PM +0800, Jason Wang wrote:
> This series tries to access virtqueue metadata through kernel virtual
> address instead of copy_user() friends since they had too much
> overheads like checks, spec barriers or even hardware feature
> toggling.

I think it's a reasonable approach.
However I need to look at whether and which mmu notifiers are invoked before
writeback. Do you know?

> Test shows about 24% improvement on TX PPS. It should benefit other
> cases as well.
>
> Changes from V2:
> - fix buggy range overlapping check
> - tear down MMU notifier during vhost ioctl to make sure invalidation
> request can read metadata userspace address and vq size without
> holding vq mutex.
> Changes from V1:
> - instead of pinning pages, use MMU notifier to invalidate vmaps and
> remap duing metadata prefetch
> - fix build warning on MIPS
>
> Jason Wang (5):
> vhost: generalize adding used elem
> vhost: fine grain userspace memory accessors
> vhost: rename vq_iotlb_prefetch() to vq_meta_prefetch()
> vhost: introduce helpers to get the size of metadata area
> vhost: access vq metadata through kernel virtual address
>
> drivers/vhost/net.c | 4 +-
> drivers/vhost/vhost.c | 416 +++++++++++++++++++++++++++++++++++++-----
> drivers/vhost/vhost.h | 15 +-
> 3 files changed, 384 insertions(+), 51 deletions(-)
>
> --
> 2.17.1