linux-kernel - Re: [PATCH] msi-x: let drivers retry when not enough vectors

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Message-Id: <200905071740.16190.sheng@linux.intel.com>
Date:	Thu, 7 May 2009 17:40:15 +0800
From:	Sheng Yang <sheng@...ux.intel.com>
To:	Matthew Wilcox <matthew@....cx>
Cc:	kvm@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>,
	jbarnes@...tuousgeek.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, Matthew Wilcox <willy@...ux.intel.com>,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] msi-x: let drivers retry when not enough vectors

On Thursday 07 May 2009 17:27:31 Matthew Wilcox wrote:
> On Thu, May 07, 2009 at 04:51:24PM +0800, Sheng Yang wrote:
> > On Thursday 07 May 2009 16:28:41 Michael S. Tsirkin wrote:
> > > pci_enable_msix currently returns -EINVAL if you ask
> > > for more vectors than supported by the device, which would
> > > typically cause fallback to regular interrupts.
> > >
> > > It's better to return the table size, making the driver retry
> > > MSI-X with less vectors.
> >
> > Hi Michael
> >
> > I think driver should read from capability list to know how many vector
> > supported by this device before enable MSI-X for device, as
> > pci_msix_table_size() did...
>
> I think Michael's patch makes sense.  It reduces the amount of work the
> driver has to do without requiring any additional work in the core.  I
> don't see the disadvantage to it.
>
> Reviewed-by: Matthew Wilcox <willy@...ux.intel.com>

It's indeed weird. Why the semantic of pci_enable_msix can be changed to 
"enable msix, or tell me how many vector do you have"? You can simply call 
pci_msix_table_size() to get what you want, also without any more work, no? I 
can't understand...

-- 
regards
Yang, Sheng

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