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

Wang, Zhihong zhihong.wang at intel.com
Tue Sep 27 18:45:24 CEST 2016



> -----Original Message-----
> From: Yuanhan Liu [mailto:yuanhan.liu at linux.intel.com]
> Sent: Tuesday, September 27, 2016 6:21 PM
> To: Jianbo Liu <jianbo.liu at linaro.org>
> 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 Thu, Sep 22, 2016 at 05:01:41PM +0800, Jianbo Liu wrote:
> > 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
> 
> There is a difference between Zhihong's code and the old I spotted in
> the first time: Zhihong removed the avail_idx prefetch. I understand
> the prefetch becomes a bit tricky when mrg-rx code path is considered;
> thus, I didn't comment on that.
> 
> That's one of the difference that, IMO, could drop a regression. I then
> finally got a chance to add it back.
> 
> A rough test shows it improves the performance of 1400B packet size greatly
> in the "txonly in host and rxonly in guest" case: +33% is the number I get
> with my test server (Ivybridge).

Thanks Yuanhan! I'll validate this on x86.

> 
> I guess this might/would help your case as well. Mind to have a test
> and tell me the results?
> 
> BTW, I made it in rush; I haven't tested the mrg-rx code path yet.
> 
> Thanks.
> 
> 	--yliu


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