Re: [PATCHv2 net-next] xen-netback: always fully coalesce guest Rx packets

[David Miller <davem@davemloft.net>]

From: David Vrabel <david.vrabel@citrix.com>
Date: Tue, 20 Jan 2015 14:49:52 +0000

> Always fully coalesce guest Rx packets into the minimum number of ring
> slots.  Reducing the number of slots per packet has significant
> performance benefits when receiving off-host traffic.
> 
> Results from XenServer's performance benchmarks:
> 
>                          Baseline    Full coalesce
> Interhost VM receive      7.2 Gb/s   11 Gb/s
> Interhost aggregate      24 Gb/s     24 Gb/s
> Intrahost single stream  14 Gb/s     14 Gb/s
> Intrahost aggregate      34 Gb/s     34 Gb/s
> 
> However, this can increase the number of grant ops per packet which
> decreases performance of backend (dom0) to VM traffic (by ~10%)
> /unless/ grant copy has been optimized for adjacent ops with the same
> source or destination (see "grant-table: defer releasing pages
> acquired in a grant copy"[1] expected in Xen 4.6).
> 
> [1] http://lists.xen.org/archives/html/xen-devel/2015-01/msg01118.html
> 
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> Acked-by: Ian Campbell <ian.campbell@citrix.com>
> ---
> Changes in v2:
> - Updated commit message with better results.

Applied, thanks David.