> -----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 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. > > Regards, > Maxime
