Subject: Re: [PATCH net-next 0/6] vhost: accelerate metadata access

From: "Michael S. Tsirkin" <[email-masked]>
Date: Wed, 5 Jun 2019 16:27:18 -0400

On Fri, May 24, 2019 at 04:12:12AM -0400, Jason Wang wrote:
> Hi:
> 
> 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 like SMAP. This is done through setup kernel address through
> direct mapping and co-opreate VM management with MMU notifiers.
> 
> Test shows about 23% improvement on TX PPS. TCP_STREAM doesn't see
> obvious improvement.
> 
> Thanks

Thanks this is queued for next.

Did you want to rebase and repost packed ring support on top?
IIUC it's on par with split ring with these patches.

> Changes from RFC V3:
> - rebase to net-next
> - Tweak on the comments
> Changes from RFC V2:
> - switch to use direct mapping instead of vmap()
> - switch to use spinlock + RCU to synchronize MMU notifier and vhost
>   data/control path
> - set dirty pages in the invalidation callbacks
> - always use copy_to/from_users() friends for the archs that may need
>   flush_dcache_pages()
> - various minor fixes
> Changes from V4:
> - use invalidate_range() instead of invalidate_range_start()
> - track dirty pages
> 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 (6):
>   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: factor out setting vring addr and num
>   vhost: access vq metadata through kernel virtual address
> 
>  drivers/vhost/net.c   |   4 +-
>  drivers/vhost/vhost.c | 850 ++++++++++++++++++++++++++++++++++++------
>  drivers/vhost/vhost.h |  38 +-
>  3 files changed, 766 insertions(+), 126 deletions(-)
> 
> -- 
> 2.18.1