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

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

> > > 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.
> 
> 

Hi Maxime,

I just did some profiling and see much higher L2 miss in vhost
dequeue with indirect_desc in my platform, indicates increase
of memory access contention.

I can keep digging further but might not be able to fix it in time
due to limited bandwidth.

Hope this helps.


Thanks
Zhihong