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

From: Jason Wang
Date: Mon Jan 07 2019 - 01:58:25 EST

On 2019/1/5 äå5:41, Michael S. Tsirkin wrote:
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

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?

I don't know but just looking at the MMU notifier ops definition, there's no such callback if my understanding is correct.


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(-)