On Tue, Oct 29, 2013 at 12:05:27PM -0700, Michael Dalton wrote:
> Agreed Eric, the buffer size should be increased so that we can accommodate a
> MTU-sized packet + mergeable virtio net header in a single buffer. I will send
> a patch to fix shortly cleaning up the #define headers as Rusty indicated and
> increasing the buffer size slightly by VirtioNet header size bytes per Eric.
>
> Jason, I'll followup with you directly - I'd like to know your exact workload
> (single steam or multi-stream netperf?), VM configuration, etc, and also see
> if
> the nit that Erichas pointed out affects your results. It is also
> worth noting that
> we may want to tune the queue sizes for your benchmarks, e.g, by reducing
> buffer size from 4KB to MTU-sized but keeping queue length constant, we're
> implicitly decreasing the number of bytes stored in the VirtioQueue for the
> VirtioNet device, so increasing the queue size may help.
>
> Best,
>
> Mike
Well we have 256 descriptors per queue, each descriptor is 16 bytes
already and they have to be physically contigious.
I don't think we can easily increase the queue size much more without
risking memory allocation failures on busy systems.
I guess one approach is to do something like:
if (queue size > 1024)
use small buffers
else
use 4K buffers.
That would reduce the risk of regressions for existing users.
--
MST
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