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Re: [Qemu-devel] [PATCH] net: add raw backend - some performance measur

From: Or Gerlitz
Subject: Re: [Qemu-devel] [PATCH] net: add raw backend - some performance measurements
Date: Mon, 20 Jul 2009 17:13:06 +0300
User-agent: Thunderbird (X11/20081209)

Jamie Lokier wrote:
> Or Gerlitz wrote:

>> the performance (packets per second and cpu utilization) one can get 
>> with bridge+tap is much lower vs what you get with the raw mode approach.

> Have you measured it?

yes, here's some data: using in the guest, 2.6.30 in the host, with 
connectivity (Intel 82575EB) between the two nodes,  I see the following 

with -net raw (packet socket)
                pps     cs      us      sys
vm->phys        240k    200     7       8       
phys->vm        160k    100     5       7

with -net tap (tap + bridge)
                pps     cs      us      sys
vm->phys        170k    600     5       10
phys->vm        150k    14k     5       20

where "pps" stands for packets-per-second, "cs", "us" and "sys" are taken from 
vmstat output, such that they represent the context switches per second, user 
and system time percents.  The benchmark I use is netperf 2.4.4 / UDP_STREAM 
with 22 bytes payload length such that there are 64(=14+20+8+22) bytes on the 
wire. On this setup (udp, 64 byte frames), doing phys->phys test, netperf 
sends/receives 450K pps and pktgen sends 900K pps, all tests done without any 
interrupt moderation tuning.

You can see that the raw mode has much better packets per second for the VM TX 
flow, and on the VM RX side, a bit better pps rate but much lower cpu 
utilization and context switches number.


All this on top of mainstream qemu whose head is commit 
"Work around Solaris gas problem"

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