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Re: [Xen-devel][Pv-ops][PATCH] Netback multiple tasklet support

To: "Xu, Dongxiao" <dongxiao.xu@xxxxxxxxx>
Subject: Re: [Xen-devel][Pv-ops][PATCH] Netback multiple tasklet support
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Thu, 10 Dec 2009 10:01:10 -0800
Cc: Steven Smith <Steven.Smith@xxxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Campbell <Ian.Campbell@xxxxxxxxxx>
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On 12/09/09 19:29, Xu, Dongxiao wrote:
Also, is it worth making it a tunable?  Presumably it needn't scale
exactly with the number of dom0 cpus; if you only have one or two gbit
interfaces, then you could saturate that pretty quickly with a small
number of cpus, regardless of how many domains you have.
How many CPUs are serving for the NIC interface is determined by how
interrupt is delivered. If system only has two gbit interfaces, and they
delivier interrupts to CPU0 and CPU1, then the case is: two CPUs handle
two tasklets. Other CPUs are idle. The group_nr just defines the max
number of tasklets, however it doesn't decide how tasklet is handled by

So does this mean that a given vcpu will be used to handle the interrupt if happens to be running on a pcpu with affinity for the device? Or that particular devices will be handled by particular vcpus?

I've pushed this out in its own branch:
xen/dom0/backend/netback-tasklet; please post any future patches
against this branch.
What's my next step for this netback-tasklet tree merging into xen/master?

Hm, well, I guess:

   * I'd like to see some comments Keir/Ian(s)/others that this is
     basically the right approach.  It looks OK to me, but I don't have
     much experience with performance in the field.
         o does nc2 make nc1 obsolete?
   * Testing to make sure it really works.  Netback is clearly critical
     functionality, so I'd like to be sure we're not introducing big


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