From mboxrd@z Thu Jan  1 00:00:00 1970
From: Luca Bigliardi <shammash@artha.org>
Subject: kvm network latency, higher with virtio ?
Date: Tue, 15 Sep 2009 17:15:09 +0200
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Hi,
I'm running some tests between two linux instances bridged together.

If I try to ping 10 times I obtain the following results:

-net nic,model=virtio -net tap :
    rtt min/avg/max/mdev = 0.756/0.967/2.115/0.389 ms

-net nic,model=rtl8139 -net tap :
    rtt min/avg/max/mdev = 0.301/0.449/1.173/0.248 ms

So it seems with virtio the latency is higher. Is it normal?

The results I'm reporting were obtained with
- host
  qemu-kvm 0.11-rc2
  kvm-kmod-2.6.30.1
  kernel: 2.6.30.5 (HIGH_RES_TIMERS=y as suggested in
                    http://www.linux-kvm.org/page/Virtio )
- guest
  kernel: 2.6.31

but I also tested older versions always obtaining latency values at least two
times higher than rtl8139/e1000 .

Thank you,
Luca