Re: [Xen-devel] [PATCH 3/3] msix restore code optimization for dom0

[Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>]

On 2013-07-24 21:55, Konrad Rzeszutek Wilk wrote:
> On Wed, Jul 24, 2013 at 11:08:43AM +0800, Zhenzhong Duan wrote:
> > PHYSDEVOP_restore_msi is used to restore all msix entrys in one hypercall
> > in dom0. But it is called multi times in current code.
> Couldn't the restore_msi_irqs instead check whether it has already
> made the hypercall (perhaps by seeing if the MSI-X's are enabled?)
> and if so don't do the hypercall?
I think it's better to remove the for loop for dom0, also hard to know 
when to clear hypercall count.
> I think you are addressing the problem from a different viewpoint.
>
> The problem is not with the API (the x86_msi one). The problem
> is with the implementation (x86_msi.restore_msi_irq - specifically
> the Xen one) having an side effect.
We have x86_msi.restore_msi_irqs and no x86_msi.restore_msi_irq,if want to
add x86_msi.restore_msi_irq, same hypercall need to be added accordingly.
> > This patch split arch_restore_msi_irqs into two functions.
> > Use arch_restore_msi_irq deal with one entry and avoid call hypercall multi
> > times in __pci_restore_msix_state.
> But irregardless of how you address the problem, this in the MSI code
> is a bit odd:
>
>         list_for_each_entry(entry, &dev->msi_list, list) {
>                 arch_restore_msi_irqs(dev, entry->irq);
>         }
>
> and if you collapse that and make the 'arch_restore_msi_irqs' be responsible
> for doing all the heavy lifting.. That does seem an improvement on the API
> and will make it inline with 'teardown_msi_irqs'.
>
> So from that view I think it would be nicer?
Yes, This patch just did that. There is 
teardown_msi_irqs/teardown_msi_irq pair.
But in current code, arch_restore_msi_irqs is used for one msix entry, 
this is not consistent with
its naming tradiition. So I changed default_restore_msi_irqs to deal 
with all entrys and
default_restore_msi_irq to deal with one entry for baremetal. For dom0, 
we have
PHYSDEVOP_restore_msi  to restore all msix entrys.

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