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Re: [Qemu-devel] KVM VM(rhel-5.5) %si is too high when TX/RX packets
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] KVM VM(rhel-5.5) %si is too high when TX/RX packets |
Date: |
Sat, 04 May 2013 09:48:05 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4 |
Il 03/05/2013 06:05, Zhanghaoyu (A) ha scritto:
> I running a VM(RHEL-5.5) on KVM hypervisor(linux-3.8 + QEMU-1.4.1), and
> direct-assign intel 82576 VF to the VM. When TX/RX packets on VM to the other
> host via iperf tool, top tool result on VM shown that the %si is too high,
> approximately 95% ~ 100%, but from the view of host, the VM's total CPU usage
> is about 20% - 30%. And the throughput rate is approximately 200Mb/s, far
> from the line rate 1Gb/s,
> And, I found the hardirq rate is lower than normal by running "watch -d -n 1
> cat /proc/interrupts", I think it's caused by the too high %si, because the
> NIC's hardirq was disabled during the softirq process.
> Then, I direct-assign the intel 82576 to the VM, the same case happened too.
> I found the intel 82576 and intel 82576 VF's interrupt mode are both
> PCI-MSI-X.
>
> And,
> I rmmod the igb driver, and, re-insmod the igb driver(igb-4.1.2) with the
> parameter IntMode=0/1(0:legacy, 1:MSI, 2:MSI-x), the problem then gone, the
> %si is approximately 20% -30%, and the throughput rate came to the line rate,
> about 940Mb/s.
> I update the VM to RHEL-6.1, the problem disappeared too.
> And, I found a very strange thing, the VM's 82576VF's irq routing is set one
> time on Vf's one interrupt received, so frequently.
RHEL 5.5 is a very old update. Can you try RHEL 5.9?
In any case, this looks a lot like a bug in the version of the driver
that was included in RHEL5.5; you should contact Red Hat support
services if you can still reproduce it with the latest RHEL5 update.
Paolo