It looks like KeSetTargetProcessorDpc(&xi->rx_dpc, 0) set the rx_dpc in VCPU0 only,
and in fact interrput for xennet are distributed across all VCPUS.
By using IntFiltr from http://support.microsoft.com/kb/252867
to set interrupt affinity to VCPU0 only, without KeSetTargetProcessorDpc
commentted, we get quite stable ping time too., which is less than 1ms
So I think this is the problem.
KeSetTargetProcessorDpc should be discard.
> Subject: RE: Rather slow time of Pin in Windows with GPL PV driver
> Date: Wed, 9 Mar 2011 22:28:48 +1100
> From: james.harper@xxxxxxxxxxxxxxxx
> To: tinnycloud@xxxxxxxxxxx
> CC: xen-devel@xxxxxxxxxxxxxxxxxxx
>
> > I may try pin later, my host has 4 * 4 core CPU.
> >
> > Well, I just compare GPL and RHEL PV driver codes, I noticed most of
> the net
> > driver
> > initialization is the same. Only one difference, in GPL code has the
> code of
> > KeSetTargetProcessorDpc(&xi->rx_dpc, 0); //in xennet_rx.c line 953
> > but the RHEL doesn't
> >
> > So I simply comments the code, recompile and did the test again.
> > The result shows good, all ping time less than < 1ms.
> >
> > May it be the cause? Is it harmful to comments this line?
> > Many thanks.
> >
>
> At a guess I would say it
should be harmful to performance, but all the
> critical code is protected by spinlocks.
>
> It could be a leftover from a previous version of GPLPV. In the current
> version, the spinlock protected code is probably a little long winded
> but is nothing compared to the passing down of packets to Windows that
> is done in the DPC but outside the spinlock.
>
> Can you do some general performance tests with this change?
>
> Is the RHEL PV driver source publicly available?
>
> James
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