On 07/21/2014 10:10 AM, Benoît Canet wrote:
The Monday 21 Jul 2014 à 09:35:29 (-0600), Chris Friesen wrote :
On 07/21/2014 09:15 AM, Benoît Canet wrote:
The Monday 21 Jul 2014 à 08:59:45 (-0600), Chris Friesen wrote :
On 07/19/2014 02:45 AM, Benoît Canet wrote:
I think in the throttling case the number of in flight operation is limited by
the emulated hardware queue. Else request would pile up and throttling would be
inefective.
So this number should be around: #define VIRTIO_PCI_QUEUE_MAX 64 or something
like than that.
Okay, that makes sense. Do you know how much data can be written as part of
a single operation? We're using 2MB hugepages for the guest memory, and we
saw the qemu RSS numbers jump from 25-30MB during normal operation up to
120-180MB when running dbench. I'd like to know what the worst-case would
Sorry I didn't understood this part at first read.
In the linux guest can you monitor:
benoit@Laure:~$ cat /sys/class/block/xyz/inflight ?
This would give us a faily precise number of the requests actually in flight
between the guest and qemu.
After a bit of a break I'm looking at this again.
While doing "dd if=/dev/zero of=testfile bs=1M count=700" in the guest,
I got a max "inflight" value of 181. This seems quite a bit higher than
VIRTIO_PCI_QUEUE_MAX.
I've seen throughput as high as ~210 MB/sec, which also kicked the RSS
numbers up above 200MB.
I tried dropping VIRTIO_PCI_QUEUE_MAX down to 32 (it didn't seem to work
at all for values much less than that, though I didn't bother getting an
exact value) and it didn't really make any difference, I saw inflight
values as high as 177.
Chris
