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
be.
I think Linux as a limit of 512Kb for io size or something like that.
So the guest would have VIRTIO_PCI_QUEUE_MAX * 512Kb of in flight buffers at
max.
Those numbers don't line up with what we were seeing...we saw a 120MB+
jump when running dbench, which would map to more like 2MB per operation
assuming a limit of VIRTIO_PCI_QUEUE_MAX (i.e. 64).
Unless there are other buffers involved that we haven't factored in...
Chris
