linux-kernel - RE: [PATCH v2 2/6] PCI/MSI: Factor out pci_get_msi

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Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6026B735D@saturn3.aculab.com>
Date:	Thu, 26 Sep 2013 09:58:53 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Alexander Gordeev" <agordeev@...hat.com>,
	"Tejun Heo" <tj@...nel.org>
Cc:	<linux-pci@...r.kernel.org>, "Joerg Roedel" <joro@...tes.org>,
	<x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<linux-ide@...r.kernel.org>, "Jan Beulich" <JBeulich@...e.com>,
	"Bjorn Helgaas" <bhelgaas@...gle.com>,
	<linuxppc-dev@...ts.ozlabs.org>, "Ingo Molnar" <mingo@...nel.org>
Subject: RE: [PATCH v2 2/6] PCI/MSI: Factor out pci_get_msi_cap() interface

> Subject: Re: [PATCH v2 2/6] PCI/MSI: Factor out pci_get_msi_cap() interface
> 
> On Wed, Sep 25, 2013 at 05:00:16PM -0400, Tejun Heo wrote:
> > Hello,
> >
> > On Wed, Sep 25, 2013 at 10:58:05PM +0200, Alexander Gordeev wrote:
> > > Unfortunately, pSeries is a shows-topper here :( It seems we have to
> > > introduce pci_get_msi{,x}_limit() interfaces to honour the quota
> > > thing.  I just hope the hardware set for pSeries is limited and we
> > > won't need to use it for all drivers.
> >
> > Can you please go into a bit of detail on that?  Why does it matter?
> 
> Because otherwise we will re-introduce a problem described by Michael:
> "We have a small number of MSIs available, limited by hardware &
> firmware, if we don't impose a quota then the first device that probes
> will get most/all of the MSIs and other devices miss out."

Would it be possible to do some kind of 2-stage allocation.
In the first pass the driver would pass a minimum and desired
number of MSI-X interrupts, but not actually be given any.
Interrupts could then be allocated after it is known how many
are required and how many are available.

	David



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