On Sun, Dec 15, 2013 at 04:20:05PM +0800, Qingshu Chen wrote:
> hi,I want to calculate the latencyof virtio in kvm, I read the document in
> http://www.linux-kvm.org/page/Virtio/Block/Latency and met some problem.
> 1. when calculating latency in kvm, the document said kvm_pio and
> kvm_set_irq can be filtered using command 'lspci -vv -nn' and 'cat
> /proc/interrupts' , but I don't know how to use the result to filter kvm_pio
> and kvm_set_irq.
Hi Qingshu,
I wrote that wiki page. The commands on the wiki are:
cd /sys/kernel/debug/tracing
echo 'port == 0xc090' >events/kvm/kvm_pio/filter
echo 'gsi == 26' >events/kvm/kvm_set_irq/filter
echo 1 >events/kvm/kvm_pio/enable
echo 1 >events/kvm/kvm_set_irq/enable
cat trace_pipe >/tmp/trace
Here is how you can find the right port and gsi values to filter:
1. The 'kvm_pio' event is used to trace guest->host virtqueue
notification. Looking at drivers/virtio/virtio_pci.c reveals that
the port is ioaddr + VIRTIO_PCI_QUEUE_NOTIFY (16).
Here is an example:
# lspci -vv -nn
00:04.0 SCSI storage controller [0100]: Red Hat, Inc Virtio block device
[1af4:1001]
[...]
Region 0: I/O ports at c080 [size=64]
Therefore you need to filter on 0xc080 + 0x10 = 0xc090 to trace
VIRTIO_PCI_QUEUE_NOTIFY accesses.
2. The 'kvm_set_irq' event is used to trace host->guest virtqueue
notifications.
Find the virtio driver instance:
# ls /sys/block/vda/device/driver/
bind module unbind virtio1
Now look up the virtqueue interrupt for 'virtio1':
# cat /proc/interrupts
[...]
185: 35129 0 0 0 0 0 8760
0 PCI-MSI-X virtio1-requests
So gsi is 185.
Stefan
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