Re: [dpdk-dev] [PATCH v4] vhost: Add indirect descriptors support to the TX path

["Wang, Zhihong" <zhihong.wang@intel.com>]

> -----Original Message-----
> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> Sent: Friday, October 28, 2016 3:42 PM
> To: Wang, Zhihong <zhihong.wang@intel.com>; Yuanhan Liu
> <yuanhan.liu@linux.intel.com>
> Cc: stephen@networkplumber.org; Pierre Pfister (ppfister)
> <ppfister@cisco.com>; Xie, Huawei <huawei.xie@intel.com>; dev@dpdk.org;
> vkaplans@redhat.com; mst@redhat.com
> Subject: Re: [dpdk-dev] [PATCH v4] vhost: Add indirect descriptors support
> to the TX path
> 
> 
> 
> On 10/28/2016 02:49 AM, Wang, Zhihong wrote:
> >
> >> > -----Original Message-----
> >> > From: Yuanhan Liu [mailto:yuanhan.liu@linux.intel.com]
> >> > Sent: Thursday, October 27, 2016 6:46 PM
> >> > To: Maxime Coquelin <maxime.coquelin@redhat.com>
> >> > Cc: Wang, Zhihong <zhihong.wang@intel.com>;
> >> > stephen@networkplumber.org; Pierre Pfister (ppfister)
> >> > <ppfister@cisco.com>; Xie, Huawei <huawei.xie@intel.com>;
> dev@dpdk.org;
> >> > vkaplans@redhat.com; mst@redhat.com
> >> > Subject: Re: [dpdk-dev] [PATCH v4] vhost: Add indirect descriptors
> support
> >> > to the TX path
> >> >
> >> > On Thu, Oct 27, 2016 at 12:35:11PM +0200, Maxime Coquelin wrote:
> >>> > >
> >>> > >
> >>> > > On 10/27/2016 12:33 PM, Yuanhan Liu wrote:
> >>>> > > >On Thu, Oct 27, 2016 at 11:10:34AM +0200, Maxime Coquelin
> wrote:
> >>>>> > > >>Hi Zhihong,
> >>>>> > > >>
> >>>>> > > >>On 10/27/2016 11:00 AM, Wang, Zhihong wrote:
> >>>>>> > > >>>Hi Maxime,
> >>>>>> > > >>>
> >>>>>> > > >>>Seems indirect desc feature is causing serious performance
> >>>>>> > > >>>degradation on Haswell platform, about 20% drop for both
> >>>>>> > > >>>mrg=on and mrg=off (--txqflags=0xf00, non-vector version),
> >>>>>> > > >>>both iofwd and macfwd.
> >>>>> > > >>I tested PVP (with macswap on guest) and Txonly/Rxonly on an
> Ivy
> >> > Bridge
> >>>>> > > >>platform, and didn't faced such a drop.
> >>>> > > >
> >>>> > > >I was actually wondering that may be the cause. I tested it with
> >>>> > > >my IvyBridge server as well, I saw no drop.
> >>>> > > >
> >>>> > > >Maybe you should find a similar platform (Haswell) and have a try?
> >>> > > Yes, that's why I asked Zhihong whether he could test Txonly in guest
> to
> >>> > > see if issue is reproducible like this.
> >> >
> >> > I have no Haswell box, otherwise I could do a quick test for you. IIRC,
> >> > he tried to disable the indirect_desc feature, then the performance
> >> > recovered. So, it's likely the indirect_desc is the culprit here.
> >> >
> >>> > > I will be easier for me to find an Haswell machine if it has not to be
> >>> > > connected back to back to and HW/SW packet generator.
> > In fact simple loopback test will also do, without pktgen.
> >
> > Start testpmd in both host and guest, and do "start" in one
> > and "start tx_first 32" in another.
> >
> > Perf drop is about 24% in my test.
> >
> 
> Thanks, I never tried this test.
> I managed to find an Haswell platform (Intel(R) Xeon(R) CPU E5-2699 v3
> @ 2.30GHz), and can reproduce the problem with the loop test you
> mention. I see a performance drop about 10% (8.94Mpps/8.08Mpps).
> Out of curiosity, what are the numbers you get with your setup?

Hi Maxime,

Let's align our test case to RC2, mrg=on, loopback, on Haswell.
My results below:
 1. indirect=1: 5.26 Mpps
 2. indirect=0: 6.54 Mpps

It's about 24% drop.

> 
> As I never tried this test, I run it again on my Sandy Bridge setup, and
> I also see a performance regression, this time of 4%.
> 
> If I understand correctly the test, only 32 packets are allocated,
> corresponding to a single burst, which is less than the queue size.
> So it makes sense that the performance is lower with this test case.

Actually it's 32 burst, so 1024 packets in total, enough to
fill the queue.

Thanks
Zhihong

> 
> Thanks,
> Maxime