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

To: Alexander Gordeev <>
Subject: Re: [PATCH RFC 00/77] Re-design MSI/MSI-X interrupts enablement pattern
From: Tejun Heo <>
Date: Wed, 9 Oct 2013 11:41:17 -0400
Cc: Benjamin Herrenschmidt <>, Ben Hutchings <>,, Bjorn Helgaas <>, Ralf Baechle <>, Michael Ellerman <>, Martin Schwidefsky <>, Ingo Molnar <>, Dan Williams <>, Andy King <>, Jon Mason <>, Matt Porter <>,,,,,,,,,,,,,, Solarflare linux maintainers <>, "VMware, Inc." <>,
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On Tue, Oct 08, 2013 at 02:22:16PM +0200, Alexander Gordeev wrote:
> If we talk about pSeries quota, then the current pSeries pci_enable_msix()
> implementation is racy internally and could fail if the quota went down
> *while* pci_enable_msix() is executing. In this case the loop will have to
> exit rather than retry with a lower number (what number?).

Ah, okay, so that one is already broken.

> In this regard the new scheme does not bring anything new and relies on
> the fact this race does not hit and therefore does not worry.
> If we talk about quota as it has to be, then yes - the loop scheme seems
> more preferable.
> Overall, looks like we just need to fix the pSeries implementation,
> if the guys want it, he-he :)

If we can't figure out a better interface for the retry case, I think
what can really help is having a simple interface for the simpler

> > 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.
> I am probably missing something here. If the global limit went down before
> inquiry then the inquiry will get what is available and try to allocate with
> than number.

Oh, I should have written between inquiry and allocation.  Sorry.



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