netdev - Re: Subject: [PATCH 1/2] x86: get back 15 vectors

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Date:	Mon, 04 Jan 2010 08:18:45 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Jesse Brandeburg <jesse.brandeburg@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	NetDEV list <netdev@...r.kernel.org>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>
Subject: Re: Subject: [PATCH 1/2] x86: get back 15 vectors

Yinghai Lu <yinghai@...nel.org> writes:

This patch is wrong.

> between FIRST_EXTERNAL_VECTOR (0x20) and FIRST_DEVICE_VECTOR (0x41)
>
> for 0x20 and 0x2f, we are safe be used_vectors will prevent it to use used one.

We can not use any of 0x20 - 0x2f for ioapic irqs.  We need the entire
priority level to ensure that the irq move cleanup ipi is of a lower
priority.

> also try to reuse 0x30 to 0x3f after smp_affinity for irq[0,15] is changed to other cpu.

There may be a point with 0x30 to 0x3f as I recall when those irqs come through a legacy
pic we need to reserve those vectors on all cpus.


Eric


> Signed-off-by: Yinghai Lu <yinghai@...nel.org>


> ---
>  arch/x86/kernel/apic/io_apic.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> Index: linux-2.6/arch/x86/kernel/apic/io_apic.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/apic/io_apic.c
> +++ linux-2.6/arch/x86/kernel/apic/io_apic.c
> @@ -1162,7 +1162,8 @@ __assign_irq_vector(int irq, struct irq_
>  	 * Also, we've got to be careful not to trash gate
>  	 * 0x80, because int 0x80 is hm, kind of importantish. ;)
>  	 */
> -	static int current_vector = FIRST_DEVICE_VECTOR, current_offset = 0;
> +	static int current_vector = FIRST_EXTERNAL_VECTOR + 1;
> +	static int current_offset = 0;
>  	unsigned int old_vector;
>  	int cpu, err;
>  	cpumask_var_t tmp_mask;
> @@ -1198,7 +1199,7 @@ next:
>  		if (vector >= first_system_vector) {
>  			/* If out of vectors on large boxen, must share them. */
>  			offset = (offset + 1) % 8;
> -			vector = FIRST_DEVICE_VECTOR + offset;
> +			vector = FIRST_EXTERNAL_VECTOR + 1 + offset;
>  		}
>  		if (unlikely(current_vector == vector))
>  			continue;
--
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