linux-kernel - Re: [PATCH 2/2] irq: Cleanup context state transitions in irq

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Date:	Sat, 23 Feb 2013 11:24:26 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/2] irq: Cleanup context state transitions in irq_exit()

On Sat, Feb 23, 2013 at 10:21 AM, Frederic Weisbecker
<fweisbec@...il.com> wrote:
>
> But tick_nohz_irq_exit() may trigger the timer softirq itself.

Suggestion: merge it with the whole softirq handler.

The softirq code *already* knows about the whole "oops, one softirq
may trigger another" issue, and has a loop - with protection against
excess - for exactly this reason. See the whole "goto restart" thing.

And tick_nohz_irq_exit() really has very similar semantics to
softiq's, it's just "CPU is idle and no pending reschedule" instead of
a softirq. But the basic rules are the same ("only run this at the
top-level context when exiting the last irq").

So maybe the right thing to do is move the whole "goto restart" one
level up, and do softirq's and tick_nohz_irq_exit both inside that
loop.

              Linus
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