On 10/31/2016 11:01 AM, Wang, Zhihong wrote: > > >> -----Original Message----- >> From: Maxime Coquelin [mailto:maxime.coquelin at redhat.com] >> Sent: Friday, October 28, 2016 3:42 PM >> To: Wang, Zhihong <zhihong.wang at intel.com>; Yuanhan Liu >> <yuanhan.liu at linux.intel.com> >> Cc: 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 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? > > 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. OK, so on my side, same setup on Haswell: 1. indirect=1: 7.44 Mpps 2. indirect=0: 8.18 Mpps
Still 10% drop in my case with mrg=on. The strange thing with both of our figures is that this is below from what I obtain with my SandyBridge machine. The SB cpu freq is 4% higher, but that doesn't explain the gap between the measurements. I'm continuing the investigations on my side. Maybe we should fix a deadline, and decide do disable indirect in Virtio PMD if root cause not identified/fixed at some point? Yuanhan, what do you think? Regards, Maxime
