> -----Original Message----- > From: Maxime Coquelin [mailto:maxime.coquelin at redhat.com] > Sent: Friday, November 4, 2016 8:54 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 11/04/2016 01:30 PM, Wang, Zhihong wrote: > > > > > >> -----Original Message----- > >> From: Maxime Coquelin [mailto:maxime.coquelin at redhat.com] > >> Sent: Friday, November 4, 2016 7:23 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 > >> > >> > >> > >>>>>> Hi Maxime, > >>>>>> > >>>>>> I did a little more macswap test and found out more stuff here: > >>>>> Thanks for doing more tests. > >>>>> > >>>>>> > >>>>>> 1. I did loopback test on another HSW machine with the same H/W, > >>>>>> and indirect_desc on and off seems have close perf > >>>>>> > >>>>>> 2. So I checked the gcc version: > >>>>>> > >>>>>> * Previous: gcc version 6.2.1 20160916 (Fedora 24) > >>>>>> > >>>>>> * New: gcc version 5.4.0 20160609 (Ubuntu 16.04.1 LTS) > >>>>> > >>>>> On my side, I tested with RHEL7.3: > >>>>> - gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-11) > >>>>> > >>>>> It certainly contains some backports from newer GCC versions. > >>>>> > >>>>>> > >>>>>> On previous one indirect_desc has 20% drop > >>>>>> > >>>>>> 3. Then I compiled binary on Ubuntu and scp to Fedora, and as > >>>>>> expected I got the same perf as on Ubuntu, and the perf gap > >>>>>> disappeared, so gcc is definitely one factor here > >>>>>> > >>>>>> 4. Then I use the Ubuntu binary on Fedora for PVP test, then the > >>>>>> perf gap comes back again and the same with the Fedora binary > >>>>>> results, indirect_desc causes about 20% drop > >>>>> > >>>>> Let me know if I understand correctly: > >>> > >>> Yes, and it's hard to breakdown further at this time. > >>> > >>> Also we may need to check whether it's caused by certain NIC > >>> model. Unfortunately I don't have the right setup right now. > >>> > >>>>> Loopback test with macswap: > >>>>> - gcc version 6.2.1 : 20% perf drop > >>>>> - gcc version 5.4.0 : No drop > >>>>> > >>>>> PVP test with macswap: > >>>>> - gcc version 6.2.1 : 20% perf drop > >>>>> - gcc version 5.4.0 : 20% perf drop > >>>> > >>>> I forgot to ask, did you recompile only host, or both host and guest > >>>> testmpd's in your test? > >> > >>> Both. > >> > >> I recompiled testpmd on a Fedora 24 machine using GCC6: > >> gcc (GCC) 6.1.1 20160621 (Red Hat 6.1.1-3) > >> Testing loopback with macswap on my Haswell RHEL7.3 machine gives me > the > >> following results: > >> - indirect on: 7.75Mpps > >> - indirect off: 7.35Mpps > >> > >> Surprisingly, I get better results with indirect on my setup (I > >> reproduced the tests multiple times). > >> > >> Do you have a document explaining the tuning/config you apply to both > >> the host and the guest (isolation, HT, hugepage size, ...) in your > >> setup? > > > > > > The setup where it goes wrong: > > 1. Xeon E5-2699, HT on, turbo off, 1GB hugepage for both host and guest > On the Haswell machine (on which I don't have BIOS access), HT is on, > but I unplug siblings at runtime. > I also have 1G pages on both sides, and I isolate the cores used by both > testpmd and vCPUS. > > > 2. Fortville 40G > > 3. Fedora 4.7.5-200.fc24.x86_64 > > 4. gcc version 6.2.1 > > 5. 16.11 RC2 for both host and guest > > 6. PVP, testpmd macswap for both host and guest > > > > BTW, I do see indirect_desc gives slightly better performance for loopback > > in tests on other platforms, but don't know how PVP performs yet. > Interesting, other platforms are also Haswell/Broadwell?
Yes, but with different OS. If you don't have the setup I can do more detailed profiling for the root cause next week, since my platform is the only one right now that reporting the drop. > > For PVP benchmarks, are your figures with 0% pkt loss? No, for testpmd perf analysis it's not necessary in my opinion. I do tried low rate though, the result is the same. > > Thanks, > Maxime > > > > > > >> > >> Regards, > >> Maxime