linux-kernel - Re: [PATCH v3] x86, irq: get correct available vectors for cpu disable

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Message-ID: <20140326185535.GE24604@oranje.fc.hp.com>
Date:	Wed, 26 Mar 2014 12:55:35 -0600
From:	Linn Crosetto <linn@...com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Prarit Bhargava <prarit@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] x86, irq: get correct available vectors for cpu
 disable

On Wed, Mar 26, 2014 at 10:04:52AM -0700, Yinghai Lu wrote:
> On Wed, Mar 26, 2014 at 9:50 AM, Linn Crosetto <linn@...com> wrote:
> > On Tue, Mar 25, 2014 at 05:18:53PM -0700, Yinghai Lu wrote:
> >
> > Just noting that not all bits above first_system_vector are set in the bitmap,
> > so the comment in asm/desc.h and the change log could be misleading:
> >
> > /* used_vectors is BITMAP for irq is not managed by percpu vector_irq */
> >
> 
> Do you mean some vector that is neither used by percpu_vector_irq nor
> system_vector
> after first_system_vector ?

Yes, that is the case. In my previous example, first_system_vector is 239, but
test_bit(240, used_vectors) would return unset, though it cannot be used by
percpu vector_irq. If it marked all vectors unusable by percpu vector_irq, then
all bits above first_system_vector would be set.

> Anyway if bit is set in used_vectors, that vector can not be used by
> percpu vector_irq.
> 
> so that statement looks still right.
> 
> Feel free to suggest right comment or changelog.

The following might be more accurate:

/* 
 * The used_vectors BITMAP marks IRQs not managed by percpu vector_irq, below
 * first_system_vector. Vectors above first_system_vector are not managed by
 * percpu vector_irq.
 */
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