linux-kernel - Re: IRQ handling difference between i386 and x86

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Message-ID: <Pine.LNX.4.64.0707010045040.9268@bizon.gios.gov.pl>
Date:	Sun, 1 Jul 2007 00:53:01 +0200 (CEST)
From:	Krzysztof Oledzki <olel@....pl>
To:	Arjan van de Ven <arjan@...radead.org>
cc:	linux-kernel@...r.kernel.org
Subject: Re: IRQ handling difference between i386 and x86_64



On Sat, 30 Jun 2007, Arjan van de Ven wrote:

> On Sat, 2007-06-30 at 16:55 +0200, Krzysztof Oledzki wrote:
>> Hello,
>>
>> It seems that IRQ handling is somehow different between i386 and x86_64.
>>
>> In my Dell PowerEdge 1950 is it possible to enable interrupts spreading
>> over all CPUs. This a single CPU, four CORE system (Quad-Core E5335 Xeon)
>> so I think that interrupts migration may be useful. Unfortunately, it
>> works only with 32-bit kernel. Booting it with x86_64 leads to situation,
>> when all interrupts goes only to the first cpu matching a smp_affinity
>> mask.
>
> arguably that is the most efficient behavior... round robin of
> interrupts is the worst possible case in terms of performance

Even on dual/quadro core CPUs with shared cache? So why it is possible to 
enable such behaviuor in BIOS, which works only on i386 BTW. :(

> are you using irqbalance ? (www.irqbalance.org)

Yes, I'm aware about this useful tool, but in some situations (routing 
for example) it cannot help much as it keeps three cpus idle. :(

Best regards,

 				Krzysztof Olędzki