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

From: "Michael S. Tsirkin" <[email-masked]>
Date: Fri, 4 Jan 2019 16:41:24 -0500

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