Subject: Re: [PATCH net-next V4 0/5] vhost: accelerate metadata access through vmap()

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 23 Jan 2019 08:58:07 -0500

On Wed, Jan 23, 2019 at 05:55:52PM +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.
> 
> Test shows about 24% improvement on TX PPS. It should benefit other
> cases as well.

ok I think this addresses most comments but it's a big change and we
just started 1.1 review so to pls give me a week to review this ok?

> Changes from V3:
> - don't try to use vmap for file backed pages
> - rebase to master
> 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 | 441 +++++++++++++++++++++++++++++++++++++-----
>  drivers/vhost/vhost.h |  15 +-
>  mm/shmem.c            |   1 +
>  4 files changed, 410 insertions(+), 51 deletions(-)
> 
> -- 
> 2.17.1