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

[Jason Wang]

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
> > 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?


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

Thanks


> > 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