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

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