linux-kernel - Re: [Xen-devel] [PATCH net-next v2 0/9] xen-netback: TX grant mapping with SKBTX_DEV

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Message-ID: <52AF26B8.2090409@citrix.com>
Date:	Mon, 16 Dec 2013 16:13:44 +0000
From:	Zoltan Kiss <zoltan.kiss@...rix.com>
To:	annie li <annie.li@...cle.com>
CC:	<ian.campbell@...rix.com>, <wei.liu2@...rix.com>,
	<xen-devel@...ts.xenproject.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <jonathan.davies@...rix.com>
Subject: Re: [Xen-devel] [PATCH net-next v2 0/9] xen-netback: TX grant mapping
 with SKBTX_DEV_ZEROCOPY instead of copy

On 16/12/13 06:32, annie li wrote:
>
> On 2013/12/13 7:48, Zoltan Kiss wrote:
>> A long known problem of the upstream netback implementation that on
>> the TX
>> path (from guest to Dom0) it copies the whole packet from guest memory
>> into
>> Dom0. That simply became a bottleneck with 10Gb NICs, and generally
>> it's a
>> huge perfomance penalty. The classic kernel version of netback used grant
>> mapping, and to get notified when the page can be unmapped, it used page
>> destructors. Unfortunately that destructor is not an upstreamable
>> solution.
>> Ian Campbell's skb fragment destructor patch series [1] tried to solve
>> this
>> problem, however it seems to be very invasive on the network stack's
>> code,
>> and therefore haven't progressed very well.
>> This patch series use SKBTX_DEV_ZEROCOPY flags to tell the stack it
>> needs to
>> know when the skb is freed up. That is the way KVM solved the same
>> problem,
>> and based on my initial tests it can do the same for us. Avoiding the
>> extra
>> copy boosted up TX throughput from 6.8 Gbps to 7.9 (I used a slower
>> Interlagos box, both Dom0 and guest on upstream kernel, on the same
>> NUMA node,
>> running iperf 2.0.5, and the remote end was a bare metal box on the
>> same 10Gb
>> switch)
> Sounds good.
> Is the TX throughput gotten between one vm and one bare metal box? or
> between multiple vms and bare metal? Do you have any test results with
> netperf?
One VM and a bare metal box. I've used only iperf.

Regards,

Zoli

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