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

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Message-Id: <20150123.175718.1746060859200808793.davem@davemloft.net>
Date:	Fri, 23 Jan 2015 17:57:18 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	david.vrabel@...rix.com
Cc:	netdev@...r.kernel.org, xen-devel@...ts.xenproject.org,
	ian.campbell@...rix.com, wei.liu2@...rix.com
Subject: Re: [PATCHv2 net-next] xen-netback: always fully coalesce guest Rx
 packets

From: David Vrabel <david.vrabel@...rix.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@...rix.com>
> Acked-by: Ian Campbell <ian.campbell@...rix.com>
> ---
> Changes in v2:
> - Updated commit message with better results.

Applied, thanks David.
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