linux-kernel - Re: [RFC 0/4] dynamically allocate arch specific system vectors

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Message-ID: <48D1AA62.6020601@zytor.com>
Date:	Wed, 17 Sep 2008 18:09:54 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
CC:	Jack Steiner <steiner@....com>, Dean Nelson <dcn@....com>,
	Ingo Molnar <mingo@...e.hu>, Alan Mayer <ajm@....com>,
	jeremy@...p.org, rusty@...tcorp.com.au, suresh.b.siddha@...el.com,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Yinghai Lu <Yinghai.lu@....com>
Subject: Re: [RFC 0/4] dynamically allocate arch specific system vectors

Eric W. Biederman wrote:
>> It is one vector for each cpu.
>>
>> It is more efficient for software if the vector # is the same for all cpus
> Why?  Especially in terms of irq counting that would seem to lead to cache
> line conflicts.
> 
>> but the software/hardware can support a unique vector for each cpu. This
>> assumes, of course, that the driver can determine the irq->vector mapping for
>> each cpu.
> 
> That sounds like you have a non-standard MSI-X vector.  You certainly have all of
> the same properties.  At which point create_irq() sounds like what you want.
> 
> One irq per cpu, per device.
> 
> It is the trend.  Don't worry all of the high performance drivers are doing it.
> That is the path that will be optimized.
> 

In particular, it's just another interrupt type.  We already have quite 
a few of those, from XT-PIC to the various IOAPIC ones, to MSI and MSI-X.

Just treating these as variants of MSI seems to me to make most sense, too.

	-hpa

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