linux-kernel - Re: [RFC PATCH v9 00/16] Provide a zero-copy method on KVM virtio-net.

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Date:	Tue, 10 Aug 2010 18:23:24 -0700
From:	Shirley Ma <mashirle@...ibm.com>
To:	xiaohui.xin@...el.com
Cc:	netdev@...r.kernel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, mst@...hat.com, mingo@...e.hu,
	davem@...emloft.net, herbert@...dor.apana.org.au,
	jdike@...ux.intel.com
Subject: Re: [RFC PATCH v9 00/16] Provide a zero-copy method on KVM
 virtio-net.

Hello Xiaohui,

On Fri, 2010-08-06 at 17:23 +0800, xiaohui.xin@...el.com wrote:
> Our goal is to improve the bandwidth and reduce the CPU usage.
> Exact performance data will be provided later. 

Have you had any performance data to share here? I tested my
experimental macvtap zero copy for TX only. The performance I have seen
as below without any tuning, (default setting):

Before: netperf 16K message size results with 60 secs run is 7.5Gb/s
over ixgbe 10GbE card. perf top shows:

2103.00 12.9% copy_user_generic_string
1541.00  9.4% handle_tx
1490.00  9.1% _raw_spin_unlock_irqrestore
1361.00  8.3% _raw_spin_lock_irqsave
1288.00  7.9% _raw_spin_lock
924.00  5.7% vhost_worker

After: netperf results with 60 secs run is 8.1Gb/s, perf output:

1093.00  9.9% _raw_spin_unlock_irqrestore
1048.00  9.5% handle_tx
934.00  8.5% _raw_spin_lock_irqsave
864.00  7.9% _raw_spin_lock
644.00  5.9% vhost_worker
387.00  3.5% use_mm 

I am still working on collecting more data (latency, cpu
utilization...). I will let you know once I get all data for macvtap TX
zero copy. Also I found some vhost performance regression on the new
kernel with tuning. I used to get 9.4Gb/s, now I couldn't get it.

Shirley

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