linux-kernel - Re: [PATCH RFC 00/77] Re-design MSI/MSI-X interrupts enablement pattern

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Date:	Tue, 08 Oct 2013 07:10:56 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Alexander Gordeev <agordeev@...hat.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Michael Ellerman <michael@...erman.id.au>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Ingo Molnar <mingo@...hat.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Andy King <acking@...are.com>, Jon Mason <jon.mason@...el.com>,
	Matt Porter <mporter@...nel.crashing.org>,
	linux-pci@...r.kernel.org, linux-mips@...ux-mips.org,
	linuxppc-dev@...ts.ozlabs.org, linux390@...ibm.com,
	linux-s390@...r.kernel.org, x86@...nel.org,
	linux-ide@...r.kernel.org, iss_storagedev@...com,
	linux-nvme@...ts.infradead.org, linux-rdma@...r.kernel.org,
	netdev@...r.kernel.org, e1000-devel@...ts.sourceforge.net,
	linux-driver@...gic.com,
	Solarflare linux maintainers <linux-net-drivers@...arflare.com>,
	"VMware, Inc." <pv-drivers@...are.com>, linux-scsi@...r.kernel.org
Subject: Re: [PATCH RFC 00/77] Re-design MSI/MSI-X interrupts enablement
 pattern

On Mon, 2013-10-07 at 14:01 -0400, Tejun Heo wrote:
> I don't think the same race condition would happen with the loop.  The
> problem case is where multiple msi(x) allocation fails completely
> because the global limit went down before inquiry and allocation.  In
> the loop based interface, it'd retry with the lower number.
> 
> As long as the number of drivers which need this sort of adaptive
> allocation isn't too high and the common cases can be made simple, I
> don't think the "complex" part of interface is all that important.
> Maybe we can have reserve / cancel type interface or just keep the
> loop with more explicit function names (ie. try_enable or something
> like that).

I'm thinking a better API overall might just have been to request
individual MSI-X one by one :-)

We want to be able to request an MSI-X at runtime anyway ... if I want
to dynamically add a queue to my network interface, I want it to be able
to pop a new arbitrary MSI-X.

And we don't want to lock drivers into contiguous MSI-X sets either.

And for the cleanup ... well that's what the "pcim" functions are for,
we can just make MSI-X variants.

Ben.


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