linux-kernel - Re: [RFC V1 RESEND 2/6] PCI/MSI: Dynamic allocation of MSI-X vectors by group

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Message-ID: <1565632489.7042.17.camel@intel.com>
Date:   Mon, 12 Aug 2019 10:54:49 -0700
From:   Megha Dey <megha.dey@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <marc.zyngier@....com>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, ashok.raj@...el.com,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [RFC V1 RESEND 2/6] PCI/MSI: Dynamic allocation of MSI-X
 vectors by group

On Sun, 2019-08-11 at 09:20 +0200, Thomas Gleixner wrote:
> On Wed, 7 Aug 2019, Marc Zyngier wrote:
> > 
> > On 07/08/2019 14:56, Thomas Gleixner wrote:
> > > 
> > > On Tue, 6 Aug 2019, Megha Dey wrote:
> > > > 
> > > > On Sat, 2019-06-29 at 09:59 +0200, Thomas Gleixner wrote:
> > > > > 
> > > > > On Fri, 21 Jun 2019, Megha Dey wrote:
> > > > Totally agreed. The request to add a dynamic MSI-X
> > > > infrastructure came
> > > > from some driver teams internally and currently they do not
> > > > have
> > > > bandwidth to come up with relevant test cases. <sigh>
> > > Hahahaha.
> > > 
> > > > 
> > > > But we hope that this patch set could serve as a precursor to
> > > > the
> > > > interrupt message store (IMS) patch set, and we can use this
> > > > patch set
> > > > as the baseline for the IMS patches.
> > > If IMS needs the same functionality, then we need to think about
> > > it
> > > slightly differently because IMS is not necessarily tied to PCI.
> > >  
> > > IMS has some similarity to the ARM GIC ITS stuff IIRC, which
> > > already
> > > provides these things outside of PCI. Marc?
> > Indeed. We have MSI-like functionality almost everywhere, and make
> > heavy
> > use of the generic MSI framework. Platform-MSI is probably the most
> > generic example we have (it's the Far West transposed to MSIs).
> > 
> > > 
> > > We probably need some generic infrastructure for this so PCI and
> > > everything
> > > else can use it.
> > Indeed. Overall, I'd like the concept of MSI on whatever bus to
> > have one
> > single behaviour across the board, as long as it makes sense for
> > that
> > bus (nobody needs another PCI MultiMSI, for example).
> Right.
> 
> @Intel: Is there documentation and perhaps early code for that IMS
> muck to
> 	look at?

Hi Thomas,

We have some early documentation on IMS which can be found here (part
of the Scalable I/O Virtualization spec):

https://software.intel.com/sites/default/files/managed/cc/0e/intel-scal
able-io-virtualization-technical-specification.pdf
(Section 3.4.1)

Also, I do have some initial IMS patches that we use internally for
testing. I will clean it up and send it as an RFC patchset shortly.
 
> 
> Thanks,
> 
> 	tglx