Subject: Re: [Xen-devel] [RFC PATCHv1 net-next] xen-netback: always fully coalesce guest Rx packets

From: Ian Campbell <[email-masked]>
Date: Tue, 20 Jan 2015 11:23:13 +0000

On Mon, 2015-01-19 at 17:36 +0000, David Vrabel wrote:
> On 13/01/15 14:30, Wei Liu wrote:
> > On Tue, Jan 13, 2015 at 02:05:17PM +0000, David Vrabel wrote:
> >> Always fully coalesce guest Rx packets into the minimum number of ring
> >> slots.  Reducing the number of slots per packet has significant
> >> performance benefits (e.g., 7.2 Gbit/s to 11 Gbit/s in an off-host
> >> receive test).
> >>
> > 
> > Good number.
> > 
> >> However, this does increase the number of grant ops per packet which
> >> decreases performance with some workloads (intrahost VM to VM)
> > 
> > Do you have figures before and after this change?
> 
> Some better (more rigorous) results done by Jonathan Davies shows no
> regressions with full coalescing even without the grant copy
> optimization, and a big improvement to single stream receive.
> 
>                          baseline    Full coalesce
> Interhost aggregate      24 Gb/s     24 Gb/s
> Interhost VM receive      7.2 Gb/s   11 Gb/s
> Intrahost single stream  14 Gb/s     14 Gb/s
> Intrahost aggregate      34 Gb/s     34 Gb/s

Do you have a third column to hand, for Full-coalesce w/ grant copy
optimisation case? (Don't worry if not)

Ian.