linux-kernel - Re: [PATCH] sched: idle: move need_resched check after function rcu_idle

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Date:	Mon, 23 Nov 2015 12:02:39 -0800
From:	Lianwei Wang <lianwei.wang@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	rjw@...ysocki.net, mingo@...hat.com
Subject: Re: [PATCH] sched: idle: move need_resched check after function rcu_idle_enter

On Mon, Nov 23, 2015 at 9:57 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Nov 23, 2015 at 09:42:06AM -0800, Lianwei Wang wrote:
>> Issue was found on ARM/Qcom platform, but I think it is applicable to
>> other platforms as well.  I add a BUG_ON after rcu_enter_idle to catch
>> it. The Qcom's cpuidle driver is not in mainline kernel yet.
>
>
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
> A: Top-posting.
> Q: What is the most annoying thing in e-mail?
>
>
> And I suspect that your qualcom thing doesn't have TIF_POLLING_NRFLAG
> either, which would introduce another need_resched() test after the
> rcu_enter_idle() call.

Sorry for the top posting and thank you for pointing it out.

I check the idle code again and realize that both the
default_idle_call and call_cpuidle will test TIF_NEED_RESCHED flag
again after rcu_enter_idle call by calling
current_clr_polling_and_test. So no issue on mainline kernel now.
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