RE: [Xen-devel] RE: Rather slow time of Pin in Windows with GPL PVdriver

["James Harper" <james.harper@xxxxxxxxxxxxxxxx>]

> 
> Yeah, you're right. We have a patch in XenServer to just use the
lowest
> numbered vCPU but in unstable it still pointlessly round robins. Thus,
if you
> bind DPCs and don't set their importance up you will end up with them
not
> being immediately scheduled quite a lot of the time.
> 

You say "pointlessly round robins"... why is the behaviour considered
pointless? (assuming you don't use bound DPCs)

I'm looking at my networking code and if I could schedule DPC's on
processors on a round-robin basis (eg because the IRQ's are submitted on
a round robin basis), one CPU could grab the rx ring lock, pull the data
off the ring into local buffers, release the lock, then process the
local buffers (build packets, submit to NDIS, etc). While the first CPU
is processing packets, another CPU can then start servicing the ring
too.

If Xen is changed to always send the IRQ to CPU zero then I'd have to
start round-robining DPC's myself if I wanted to do it that way...

Currently I'm suffering a bit from the small ring sizes not being able
to hold enough buffers to keep packets flowing quickly in all
situations.

James

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