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

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Date:	Wed, 11 Feb 2009 10:34:39 -0800
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	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>,
	"kaneshige.kenji@...fujitsu.com" <kaneshige.kenji@...fujitsu.com>
Subject: RE: [PATCH 0/8] git pull request for tip/tracing/core

> The bits in question is really the number of possible nested interrupts
> that can happen. We take the paranoid approach that we can have a max
> nesting of NR_IRQS. Perhaps this can be changed, and just do a max of
> 1<<10 nesting? And have a big warn on if it happens to be bigger, or fall
> to another counter if it is bigger.
>
> 1000 nested IRQs seems a bit extreme :-/

Ah, I see.  Then the answer is very different.  The number of nested
interrupts possible on a cpu is limited by the number of priority
classes for interrupts (See Table 5-8 on page 2:112 of the Itanium
software developers manual).  Effectively the max nesting depth is
16.

1000 nested interrupts would be certain to run us out of stack.

-Tony
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