On 10/28/2016 02:49 AM, Wang, Zhihong wrote: > >> > -----Original Message----- >> > From: Yuanhan Liu [mailto:yuanhan.liu at linux.intel.com] >> > Sent: Thursday, October 27, 2016 6:46 PM >> > To: Maxime Coquelin <maxime.coquelin at redhat.com> >> > Cc: Wang, Zhihong <zhihong.wang at intel.com>; >> > stephen at networkplumber.org; Pierre Pfister (ppfister) >> > <ppfister at cisco.com>; Xie, Huawei <huawei.xie at intel.com>; dev at >> > dpdk.org; >> > vkaplans at redhat.com; mst at 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? 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. Thanks, Maxime
