linux-kernel - Re: [patch 26/26] x64, x2apic/intr-remap: introduce CONFIG_INTR

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Date:	Thu, 10 Jul 2008 18:53:42 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Yong Wang <yong.y.wang@...ux.intel.com>
Cc:	Suresh Siddha <suresh.b.siddha@...el.com>, mingo@...e.hu,
	hpa@...or.com, tglx@...utronix.de, akpm@...ux-foundation.org,
	arjan@...ux.intel.com, andi@...stfloor.org,
	jbarnes@...tuousgeek.org, steiner@....com,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 26/26] x64, x2apic/intr-remap: introduce CONFIG_INTR_REMAP

Yong Wang <yong.y.wang@...ux.intel.com> writes:

> Yes, it is possible to run in x2apic mode without intr-remap. However, the
> extended
> cpu addressability will not be fully utilized that way.

Thanks.  I can see that as there are only about 16bits for the cpuid
in the irq routing entries.

Still it looks like we should enable x2apic if we can (as it is more
optimized) and should be faster.  Then if we have x2apic support
enable irq remapping if we can, although I'm not positive x2apic
support is required for the irq remapping.

Ultimately we should also enable directed ack when available instead
of broadcast ack for level triggered ioapic irqs.  That should also
reduce some rare but potentially unnecessary traffic.

Eric

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