linux-kernel - Re: [PATCH 2/3] x86: x2apic/cluster: Make use of lowest priority delivery mode

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Message-ID: <20120518144153.GD8455@moon>
Date:	Fri, 18 May 2012 18:41:53 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Alexander Gordeev <agordeev@...hat.com>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Yinghai Lu <yinghai@...nel.org>
Subject: Re: [PATCH 2/3] x86: x2apic/cluster: Make use of lowest priority
 delivery mode

On Fri, May 18, 2012 at 12:26:41PM +0200, Alexander Gordeev wrote:
> Currently x2APIC in logical destination mode delivers interrupts to a
> single CPU, no matter how many CPUs were specified in the destination
> cpumask.
> 
> This fix enables delivery of interrupts to multiple CPUs by bit-ORing
> Logical IDs of destination CPUs that have matching Cluster ID.
> 
> Because only one cluster could be specified in a message destination
> address, the destination cpumask is tried for a cluster that contains
> maximum number of CPUs matching this cpumask. The CPUs in this cluster
> are selected to receive the interrupts while all other CPUs (in the
> cpumask) are ignored.

Hi Alexander,

I'm a bit confused, we do compose destination id from target cpumask
and send one ipi per _cluster_ with all cpus belonging to this cluster
OR'ed. So if my memory doesn't betray me all specified cpus in cluster
should obtain this message. Thus I'm wondering where do you find that
only one apic obtains ipi? (note i don't have the real physical
machine with x2apic enabled handy to test, so please share
the experience).

	Cyrill
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