linux-kernel - RE: IRQ affinity enforced only after first interrupt.

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Date:	Mon, 26 Mar 2012 21:04:20 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Yevgeny Petrilin <yevgenyp@...lanox.com>
cc:	Jiang Liu <liuj97@...il.com>, Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Yael Shenhav <yaeli@...lanox.com>
Subject: RE: IRQ affinity enforced only after first interrupt.

On Mon, 26 Mar 2012, Yevgeny Petrilin wrote:

> > 
> > The architecture specific code will determine whether the IRQ could be migrated
> > in process context. For example, the IRQ_MOVE_PCNTXT flag will be set on x86
> > systems if interrupt remapping is enabled.
>
> Actually I am encountering this issue with x86, and see different
> behavior with different HW devices (NICs). On same machine I have
> one device that responds immediately to affinity changes while the
> other one changes the affinity only after first interrupt.

That simply depends on the underlying hardware. On certain hardware we
can change the affinity only in hard interrupt context, that means
right when a interrupt of that device is delivered.

On the other devices we can change it right away and the corresponding
interrupt chips set IRQ_MOVE_PCNTXT to indicate that.

There is nothing we can do about this. It's dictated by hardware.

Thanks,

	tglx
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