linux-kernel - Re: [PATCH 0/8] git pull request for tip/tracing/core

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Date:	Thu, 12 Feb 2009 12:15:35 +0900
From:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	"Luck, Tony" <tony.luck@...el.com>, Ingo Molnar <mingo@...e.hu>,
	Mike Travis <travis@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"isimatu.yasuaki@...fujitsu.com" <isimatu.yasuaki@...fujitsu.com>
Subject: Re: [PATCH 0/8] git pull request for tip/tracing/core

Steven Rostedt wrote:
> On Thu, 12 Feb 2009, Kenji Kaneshige wrote:
>> Luck, Tony wrote:
>>>>> Before we go and make the change, Peter brought up a good point on IRC. Is
>>>>> there any reason that ia64 needs 1 << 14 IRQs?  That's 16384!
>>>>>
>>>>> Perhaps the better solution wolud be (if possible), to simply lower the
>>>>> number of bits.
>>>> i'm the wrong person to be asked about that. (Cc:-ed the right people)
>>> People build some pretty big systems on ia64.  SGI's largest has 4096
>>> cpus ... so 16384 IRQs is only 4 per cpu.  That doesn't sound like very
>>> many to me.
>>>
>>> Fujitsu added the vector domain support for ia64 to get around the shortage
>>> of IRQs for large machines.  Added them to the Cc: list to see if they have
>>> comments on how many IRQs are needed.
>>>
>> The 1024 IRQs are enough for GSIs on our maximum configuration. But
>> if the devices are MSI/MSI-X capable, it could be more than 1024. 
> 
> But you would never expect more than 1024 nested interrupts all on the 
> same CPU?  That is, to have over 1024 interrupts interrupting each other?
> 

Itanium processor has 240 vectors for external interrupts and
has a mechanism to classifies them to 16 priority classes. The
ia64 linux limits maximum nested interrupts depth to 16 using
this mechanism.

Thanks,
Kenji Kaneshige


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