-----Original Message-----
From: Wang, Zhihong
Sent: Tuesday, August 23, 2016 10:31 AM
To: Maxime Coquelin <redacted>; dev@dpdk.org
Cc: yuanhan.liu@linux.intel.com
Subject: RE: [PATCH v3 0/5] vhost: optimize enqueue

quoted

-----Original Message-----
From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
Sent: Monday, August 22, 2016 6:02 PM
To: Wang, Zhihong <redacted>; dev@dpdk.org
Cc: yuanhan.liu@linux.intel.com
Subject: Re: [PATCH v3 0/5] vhost: optimize enqueue


On 08/22/2016 10:11 AM, Maxime Coquelin wrote:

quoted

Hi Zhihong,

On 08/19/2016 07:43 AM, Zhihong Wang wrote:

quoted

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:

 *  For fast frontends (eg. DPDK virtio pmd), higher performance

(maximum

quoted

quoted

    throughput) can be achieved.

 *  For slow frontends (eg. kernel virtio-net), better scalability can be
    achieved, each vhost core can support more connections since it takes
    less cycles to handle each single frontend.

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.

Thanks for these details, this is helpful to understand where the perf
gain comes from.
I would suggest to add these information as comments in the code
where/if it makes sense. If more a general comment, at least add it in
the commit message of the patch introducing it.
Indeed, adding it to the cover letter is fine, but the information is
lost as soon as the series is applied.

You don't mention any figures, so I set up a benchmark on my side to
evaluate your series. It indeed shows an interesting performance gain.

My setup consists of one host running a guest.
The guest generates as much 64bytes packets as possible using
pktgen-dpdk. The hosts forwards received packets back to the guest
using testpmd on vhost pmd interface. Guest's vCPUs are pinned to
physical CPUs.

I tested it with and without your v1 patch, with and without
rx-mergeable feature turned ON.
Results are the average of 8 runs of 60 seconds:

Rx-Mergeable ON : 7.72Mpps
Rx-Mergeable ON + "vhost: optimize enqueue" v1: 9.19Mpps
Rx-Mergeable OFF: 10.52Mpps
Rx-Mergeable OFF + "vhost: optimize enqueue" v1: 10.60Mpps

I forgot to add that before this series, I think we should first fix the windows

bug.

quoted

Else we will need a dedicated fix for the stable branch.

Okay I'll try to fix it, though I can't make any promises at present.

Have tried once but stopped since we don't have enough debug info from the
frontend side so basically I was debugging the backend based on guesses.

Hi Maxime, Yuanhan,

I've identified the root cause, do you think it makes sense to put the fix
in the same patch set? Or send it as a separated patch?


Thanks
Zhihong

quoted

Regards,
Maxime