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

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Message-ID: <CAFTL4hyYRO3MGBy9SgCvB+jhBTtW=RH3Pb4cXGpYMQJfCa3M5g@mail.gmail.com>
Date:	Tue, 26 Feb 2013 15:28:34 +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 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.
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