linux-kernel - Re: [PATCH 1/1] irq: Maintain user set affinity

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Date:	Thu, 6 Nov 2008 17:23:51 -0600
From:	Kumar Gala <galak@...nel.crashing.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, linuxppc-dev@...abs.org
Subject: Re: [PATCH 1/1] irq: Maintain user set affinity


On Nov 6, 2008, at 3:35 PM, Andrew Morton wrote:

> On Tue, 4 Nov 2008 10:31:05 -0600 (CST)
> Kumar Gala <galak@...nel.crashing.org> wrote:
>
>>> From 819ad3ed4660f4238e053728a8b5aa93d22b13d7 Mon Sep 17 00:00:00  
>>> 2001
>> From: Kumar Gala <galak@...nel.crashing.org>
>> Date: Tue, 4 Nov 2008 10:13:53 -0600
>> Subject: [PATCH 1/1] irq: Maintain user set affinity
>>
>> This addresses a regression in that if a user specified an affinity
>> for an interrupt that affinity information would get reset between
>> a request_irq(), free_irq() and request_irq() for the same irq.
>>
>> On example of this is bringing up an ethernet interface, taking
>> it down and bringing it back up again.
>>
>> Instead of always using the irq_default_affinity we use the
>> previous setting of the IRQs affinity with the assumption that
>> at boot the IRQs affinity will be set to irq_default_affinity.
>>
>> Signed-off-by: Kumar Gala <galak@...nel.crashing.org>
>> ---
>> kernel/irq/manage.c |    7 +++++--
>> 1 files changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
>> index c498a1b..ea7d11b 100644
>> --- a/kernel/irq/manage.c
>> +++ b/kernel/irq/manage.c
>> @@ -115,9 +115,12 @@ int irq_select_affinity(unsigned int irq)
>> 	if (!irq_can_set_affinity(irq))
>> 		return 0;
>>
>> -	cpus_and(mask, cpu_online_map, irq_default_affinity);
>> -
>> 	desc = irq_to_desc(irq);
>> +
>> +	mask = desc->affinity;
>> +
>> +	cpus_and(mask, cpu_online_map, mask);
>> +
>> 	desc->affinity = mask;
>> 	desc->chip->set_affinity(irq, mask);
>>
>
> Are you able to identify when this regression occurred?  It isn't
> immediately obvious to me.
>
> If the regression is present in 2.6.27 or earlier, do you think we
> should backport the fix?  If so, a different patch would be needed due
> to the presence of
>
> commit 08678b0841267c1d00d771fe01548d86043d065e
> Author: Yinghai Lu <yhlu.kernel@...il.com>
> Date:   Tue Aug 19 20:50:05 2008 -0700
>
>    generic: sparse irqs: use irq_desc() together with dyn_array,  
> instead of irq_desc[]

It didn't creep in during 2.6.27.  I will back port a patch to  
2.6.27.  Thomas has provided me a better patch that handles a few  
critical issues that mine doesn't.  I'll be testing it this evening  
and will backport to 2.6.27 if it works out.

- k
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