[dpdk-dev] [PATCH v3 0/5] vhost: optimize enqueue

[Jianbo Liu]

On 22 September 2016 at 18:04, Wang, Zhihong <zhihong.wang at intel.com> wrote:
>
>
>> -----Original Message-----
>> From: Jianbo Liu [mailto:jianbo.liu at linaro.org]
>> Sent: Thursday, September 22, 2016 5:02 PM
>> To: Wang, Zhihong <zhihong.wang at intel.com>
>> Cc: Yuanhan Liu <yuanhan.liu at linux.intel.com>; Maxime Coquelin
>> <maxime.coquelin at redhat.com>; dev at dpdk.org
>> Subject: Re: [dpdk-dev] [PATCH v3 0/5] vhost: optimize enqueue
>>
>> On 22 September 2016 at 14:58, Wang, Zhihong <zhihong.wang at intel.com>
>> wrote:
>> >
>> >
>> >> -----Original Message-----
>> >> From: Jianbo Liu [mailto:jianbo.liu at linaro.org]
>> >> Sent: Thursday, September 22, 2016 1:48 PM
>> >> To: Yuanhan Liu <yuanhan.liu at linux.intel.com>
>> >> Cc: Wang, Zhihong <zhihong.wang at intel.com>; Maxime Coquelin
>> >> <maxime.coquelin at redhat.com>; dev at dpdk.org
>> >> Subject: Re: [dpdk-dev] [PATCH v3 0/5] vhost: optimize enqueue
>> >>
>> >> On 22 September 2016 at 10:29, Yuanhan Liu
>> <yuanhan.liu at linux.intel.com>
>> >> wrote:
>> >> > On Wed, Sep 21, 2016 at 08:54:11PM +0800, Jianbo Liu wrote:
>> >> >> >> > My setup consists of one host running a guest.
>> >> >> >> > The guest generates as much 64bytes packets as possible using
>> >> >> >>
>> >> >> >> Have you tested with other different packet size?
>> >> >> >> My testing shows that performance is dropping when packet size is
>> >> more
>> >> >> >> than 256.
>> >> >> >
>> >> >> >
>> >> >> > Hi Jianbo,
>> >> >> >
>> >> >> > Thanks for reporting this.
>> >> >> >
>> >> >> >  1. Are you running the vector frontend with mrg_rxbuf=off?
>> >> >> >
>> >> Yes, my testing is mrg_rxbuf=off, but not vector frontend PMD.
>> >>
>> >> >> >  2. Could you please specify what CPU you're running? Is it Haswell
>> >> >> >     or Ivy Bridge?
>> >> >> >
>> >> It's an ARM server.
>> >>
>> >> >> >  3. How many percentage of drop are you seeing?
>> >> The testing result:
>> >> size (bytes)     improvement (%)
>> >> 64                   3.92
>> >> 128                 11.51
>> >> 256                  24.16
>> >> 512                  -13.79
>> >> 1024                -22.51
>> >> 1500                -12.22
>> >> A correction is that performance is dropping if byte size is larger than 512.
>> >
>> >
>> > Jianbo,
>> >
>> > Could you please verify does this patch really cause enqueue perf to drop?
>> >
>> > You can test the enqueue path only by set guest to do rxonly, and compare
>> > the mpps by show port stats all in the guest.
>> >
>> >
>> Tested with testpmd, host: txonly, guest: rxonly
>> size (bytes)     improvement (%)
>> 64                    4.12
>> 128                   6
>> 256                   2.65
>> 512                   -1.12
>> 1024                 -7.02
>
>
>
> I think your number is little bit hard to understand for me, this patch's
> optimization contains 2 parts:
>
>  1. ring operation: works for both mrg_rxbuf on and off
>
>  2. remote write ordering: works for mrg_rxbuf=on only
>
> So, for mrg_rxbuf=off, if this patch is good for 64B packets, then it
> shouldn't do anything bad for larger packets.
>
> This is the gain on x86 platform: host iofwd between nic and vhost,
> guest rxonly.
>
> nic2vm  enhancement
> 64      21.83%
> 128     16.97%
> 256     6.34%
> 512     0.01%
> 1024    0.00%
>
I bootup a VM with 2 virtual port, and stress the traffic between them.
First, I stressed with pktgen-dpdk in VM, and did iofwd in host.
Then, as you told, I did rxonly in VM, and txonly in host.

> I suspect there's some complication in ARM's micro-arch.
>
> Could you try v6 and apply all patches except the the last one:
> [PATCH v6 6/6] vhost: optimize cache access
>
> And see if there's still perf drop?
>
The last patch can improve the performance. The drop is actually
caused by the second patch.

Jianbo