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

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Message-ID: <953B660C027164448AE903364AC447D2618E24BF@MTLDAG02.mtl.com>
Date:	Tue, 27 Mar 2012 09:39:08 +0000
From:	Yevgeny Petrilin <yevgenyp@...lanox.com>
To:	Thomas Gleixner <tglx@...utronix.de>
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.

> > >
> > > 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 for the explanation,
Which capabilities of the HW show whether IRQ_MOVE_PCNTXT can be set or not?
Is it done by reading configuration from PCI?

Thanks,
Yevgeny
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