Message-ID: <4C525CD2.5080604@redhat.com>
Date: Fri, 30 Jul 2010 08:02:10 +0300
From: Avi Kivity <avi@redhat.com>
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To: Shirley Ma <mashirle@us.ibm.com>
CC: xiaohui.xin@intel.com, netdev@vger.kernel.org, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, mst@redhat.com, mingo@elte.hu,
        davem@davemloft.net, herbert@gondor.hengli.com.au,
        jdike@linux.intel.com
Subject: Re: [RFC PATCH v8 00/16] Provide a zero-copy method on KVM virtio-net.
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  On 07/30/2010 01:31 AM, Shirley Ma wrote:
>
>> Our goal is to improve the bandwidth and reduce the CPU usage.
>> Exact performance data will be provided later.
> I did some vhost performance measurement over 10Gb ixgbe, and found that
> in order to get consistent BW results, netperf/netserver, qemu, vhost
> threads smp affinities are required.
>
> Looking forward to these results for small message size comparison. For
> large message size 10Gb ixgbe BW already reached by doing vhost smp
> affinity w/i offloading support, we will see how much CPU utilization it
> can be reduced.
>
> Please provide latency results as well. I did some experimental on
> macvtap zero copy sendmsg, what I have found that get_user_pages latency
> pretty high.
>

get_user_pages() is indeed slow.  But what about get_user_pages_fast()?

Note that when the page is first touched, get_user_pages_fast() falls 
back to get_user_pages(), so the latency needs to be measured after 
quite a bit of warm-up.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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