linux-kernel - Re: [PATCH 3/3] msix restore code optimization for dom0

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Date:	Thu, 25 Jul 2013 08:28:14 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Zhenzhong Duan <zhenzhong.duan@...cle.com>
Cc:	linux-pci@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	xen-devel <xen-devel@...ts.xen.org>, bhelgaas@...gle.com,
	Feng Jin <joe.jin@...cle.com>,
	"x86@...nel.org >> \"x86@...nel.org\"" <x86@...nel.org>
Subject: Re: [PATCH 3/3] msix restore code optimization for dom0

On Thu, Jul 25, 2013 at 03:17:29PM +0800, Zhenzhong Duan wrote:
> 
> 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.

I think you need to repost this then without any mention to the
implementation  and just point out that the reason for doing the cleanup
from an API perspective.

And also change the title. Thanks
 
> >
> >>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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