Hi Maxime,
Do you have more comments about this set? If no, I think I could merge
it shortly.
Thanks.
--yliu
On Mon, Sep 19, 2016 at 10:00:11PM -0400, Zhihong Wang wrote:
> This patch set optimizes the vhost enqueue function.
>
> It implements the vhost logic from scratch into a single function designed
> for high performance and good maintainability, and improves CPU efficiency
> significantly by optimizing cache access, which means:
>
> * Higher maximum throughput can be achieved for fast frontends like DPDK
> virtio pmd.
>
> * Better scalability can be achieved that each vhost core can support
> more connections because it takes less cycles to handle each single
> frontend.
>
> This patch set contains:
>
> 1. A Windows VM compatibility fix for vhost enqueue in 16.07 release.
>
> 2. A baseline patch to rewrite the vhost logic.
>
> 3. A series of optimization patches added upon the baseline.
>
> The main optimization techniques are:
>
> 1. Reorder code to reduce CPU pipeline stall cycles.
>
> 2. Batch update the used ring for better efficiency.
>
> 3. Prefetch descriptor to hide cache latency.
>
> 4. Remove useless volatile attribute to allow compiler optimization.
>
> Code reordering and batch used ring update bring most of the performance
> improvements.
>
> In the existing code there're 2 callbacks for vhost enqueue:
>
> * virtio_dev_merge_rx for mrg_rxbuf turned on cases.
>
> * virtio_dev_rx for mrg_rxbuf turned off cases.
>
> The performance of the existing code is not optimal, especially when the
> mrg_rxbuf feature turned on. Besides, having 2 callback paths increases
> maintenance efforts.
>
> Also, there's a compatibility issue in the existing code which causes
> Windows VM to hang when the mrg_rxbuf feature turned on.
>
> ---
> Changes in v6:
>
> 1. Merge duplicated code.
>
> 2. Introduce a function for used ring write.
>
> 3. Add necessary comments.
>
> ---
> Changes in v5:
>
> 1. Rebase to dpdk-next-virtio master.
>
> 2. Rename variables to keep consistent in naming style.
>
> 3. Small changes like return value adjustment and vertical alignment.
>
> 4. Add details in commit log.
>
> ---
> Changes in v4:
>
> 1. Fix a Windows VM compatibility issue.
>
> 2. Free shadow used ring in the right place.
>
> 3. Add failure check for shadow used ring malloc.
>
> 4. Refactor the code for clearer logic.
>
> 5. Add PRINT_PACKET for debugging.
>
> ---
> Changes in v3:
>
> 1. Remove unnecessary memset which causes frontend stall on SNB & IVB.
>
> 2. Rename variables to follow naming convention.
>
> 3. Rewrite enqueue and delete the obsolete in the same patch.
>
> ---
> Changes in v2:
>
> 1. Split the big function into several small ones.
>
> 2. Use multiple patches to explain each optimization.
>
> 3. Add comments.
>
> Zhihong Wang (6):
> vhost: fix windows vm hang
> vhost: rewrite enqueue
> vhost: remove useless volatile
> vhost: add desc prefetch
> vhost: batch update used ring
> vhost: optimize cache access
>
> lib/librte_vhost/vhost.c | 20 +-
> lib/librte_vhost/vhost.h | 6 +-
> lib/librte_vhost/vhost_user.c | 31 ++-
> lib/librte_vhost/virtio_net.c | 541
> ++++++++++++++----------------------------
> 4 files changed, 225 insertions(+), 373 deletions(-)
>
> --
> 2.7.4
