linux-kernel - Re: [PATCH net-next RFC 0/5] batched tx processing in vhost

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Date:   Tue, 26 Sep 2017 16:45:54 +0300
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH net-next RFC 0/5] batched tx processing in vhost_net

On Fri, Sep 22, 2017 at 04:02:30PM +0800, Jason Wang wrote:
> Hi:
> 
> This series tries to implement basic tx batched processing. This is
> done by prefetching descriptor indices and update used ring in a
> batch. This intends to speed up used ring updating and improve the
> cache utilization.

Interesting, thanks for the patches. So IIUC most of the gain is really
overcoming some of the shortcomings of virtio 1.0 wrt cache utilization?

Which is fair enough (1.0 is already deployed) but I would like to avoid
making 1.1 support harder, and this patchset does this unfortunately,
see comments on individual patches. I'm sure it can be addressed though.

> Test shows about ~22% improvement in tx pss.

Is this with or without tx napi in guest?

> Please review.
> 
> Jason Wang (5):
>   vhost: split out ring head fetching logic
>   vhost: introduce helper to prefetch desc index
>   vhost: introduce vhost_add_used_idx()
>   vhost_net: rename VHOST_RX_BATCH to VHOST_NET_BATCH
>   vhost_net: basic tx virtqueue batched processing
> 
>  drivers/vhost/net.c   | 221 ++++++++++++++++++++++++++++----------------------
>  drivers/vhost/vhost.c | 165 +++++++++++++++++++++++++++++++------
>  drivers/vhost/vhost.h |   9 ++
>  3 files changed, 270 insertions(+), 125 deletions(-)
> 
> -- 
> 2.7.4