Re: [PATCH net-next] virtio-net: enable multiqueue by default

On 2016年11月25日 12:43, Michael S. Tsirkin wrote:

On Fri, Nov 25, 2016 at 12:37:26PM +0800, Jason Wang wrote:

quoted

quoted

We use single queue even if multiqueue is enabled and let admin to
enable it through ethtool later. This is used to avoid possible
regression (small packet TCP stream transmission). But looks like an
overkill since:

- single queue user can disable multiqueue when launching qemu
- brings extra troubles for the management since it needs extra admin
  tool in guest to enable multiqueue
- multiqueue performs much better than single queue in most of the
  cases

So this patch enables multiqueue by default: if #queues is less than or
equal to #vcpu, enable as much as queue pairs; if #queues is greater
than #vcpu, enable #vcpu queue pairs.

Cc: Hannes Frederic Sowa<redacted>
Cc: Michael S. Tsirkin<mst@redhat.com>
Cc: Neil Horman<redacted>
Cc: Jeremy Eder<redacted>
Cc: Marko Myllynen<redacted>
Cc: Maxime Coquelin<redacted>
Signed-off-by: Jason Wang<redacted>

OK at some level but all uses of num_online_cpus()
like this are racy versus hotplug.
I know we already have this bug but shouldn't we fix it
before we add more?

Not sure I get the point, do you mean adding get/put_online_cpus()? But 
is it a real bug? We don't do any cpu specific things so I believe it's 
not necessary (unless we want to keep #queues == #vcpus magically but I 
don't think so). Admin need to re-configure #queues after cpu hotplug if 
they wish.

Thanks
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