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

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Date:	Tue, 26 Feb 2013 17:27:30 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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()

2013/2/26 Thomas Gleixner <tglx@...utronix.de>:
>
> On Tue, 26 Feb 2013, Frederic Weisbecker wrote:
>
>> 2013/2/26 Thomas Gleixner <tglx@...utronix.de>:
>> > On Fri, 22 Feb 2013, Linus Torvalds wrote:
>> >> On Fri, Feb 22, 2013 at 7:06 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
>> >> >>
>> >> >> I prefer to let you guys have the final word on this patch. Whether you
>> >> >> apply it or not, I fear I'll never be entirely happy either way :)
>> >> >> That's the sad fate of dealing with circular dependencies...
>> >> >
>> >> > plus the butt ugly softirq semantics or the lack thereof ...
>> >>
>> >> The softirq semantics are perfectly fine. Don't blame softirq for the
>> >> fact that irq_exit() has had shit-for-brains for a long time.
>> >>
>> >> Just move the whole "invoke_softirq()" thing down to *after* the
>> >> tick_nohz_irq_exit() stuff.
>> >
>> > We can't move tick_nohz_irq_exit() before invoke_softirq() simply
>> > because we need to take the timers into account for NOHZ and those can
>> > change when the softirq code runs.
>> >
>> > So no, we need an extra check after invoke_softirq() and the same is
>> > true for RCU.
>>
>> And what do you think about Linus's idea to move tick_nohz_irq_exit()
>> to do_softirq()?
>> This sounds feasible and a right place to do this, I hope that won't
>> uglify do_softirq() though.
>> I can try something.
>
> Yeah, looks doable. the rcu stuff needs to go there as well, right?

Probably. I'll try something.
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