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

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Message-ID: <54BE3E43.3010405@citrix.com>
Date:	Tue, 20 Jan 2015 11:38:43 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
CC:	<netdev@...r.kernel.org>, <xen-devel@...ts.xenproject.org>,
	Wei Liu <wei.liu2@...rix.com>
Subject: Re: [RFC PATCHv1 net-next] xen-netback: always fully coalesce guest
 Rx packets

On 20/01/15 11:34, Ian Campbell wrote:
> On Tue, 2015-01-13 at 14:05 +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).
>>
>> However, this does increase the number of grant ops per packet which
>> decreases performance with some workloads (intrahost VM to VM)
>> /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]).
>>
>> Do we need to retain the existing path and make the always coalesce
>> path conditional on a suitable version of Xen?
>>
>> [1] http://lists.xen.org/archives/html/xen-devel/2015-01/msg01118.html
>>
>> Signed-off-by: David Vrabel <david.vrabel@...rix.com>
> 
> Looks good to me, thanks. Based on that plus the conversation in the
> other subthread:
> 
> Acked-by: Ian Campbell <ian.campbell@...rix.com>

Thanks.  I'll resend with a better commit message.

David
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