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

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: netdev@vger.kernel.org, davem@davemloft.net,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	virtualization@lists.linux-foundation.org
Subject: Re: [RFC PATCH V3 0/5] Hi:
Date: Wed, 2 Jan 2019 15:47:09 -0500	[thread overview]
Message-ID: <20190102154038-mutt-send-email-mst__42922.3771593117$1546461915$gmane$org@kernel.org> (raw)
In-Reply-To: <20181229124656.3900-1-jasowang@redhat.com>

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.

Will review, thanks!
One questions that comes to mind is whether it's all about bypassing
stac/clac.  Could you please include a performance comparison with
nosmap?

> 
> 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