linux-kernel - Re: [PATCH 16/20] sched/idle: Use explicit broadcast oneshot control function

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Message-ID: <CACRpkdZUS9Qj25waYHWUNeeVS3QiK3+QFc-CEgwUPqGd_cEDCg@mail.gmail.com>
Date:	Wed, 29 Apr 2015 09:10:18 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Sudeep Holla <sudeep.holla@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH 16/20] sched/idle: Use explicit broadcast oneshot control function

On Wed, Apr 29, 2015 at 3:04 AM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Wednesday, April 29, 2015 02:50:22 AM Rafael J. Wysocki wrote:

>> Below is the patch I came up with in the meantime.
>>
>> This moves the "switch to broadcast" timer logic into
>> cpuidle_enter_state() which allows tick_broadcast_exit() to be
>> called directly with interrupts disabled (as required), but
>> it also adds a fallback branch reflecting the 4.0 and earlier
>> behavior for idle states that enable interrupts on exit
>> from their ->enter callbacks.
>>
>> I'm not aware of any valid cases when CPUIDLE_FLAG_TIMER_STOP can be
>> set for such states, but people may try to add stuff like that in the
>> future, so it's better to catch that (hence the WARN_ON_ONCE) and do
>> our best to handle it gracefully anyway, IMO.
>>
>> The "if (entered_state == -EBUSY)" check is conservative.  It may
>> be better to do "if (entered_state < 0)" and fall back to the default
>> on all errors, but that's not what we do today (I guess the concern
>> would be "what if the state ->enter returns an error after entering
>> and exiting the idle state, in which case we may miss a wakeup event
>> if we fall back to the default").
>
> Actually, if my understanding of things is correct (the local clock event
> device cannot go away from under code executed with interrupts disabled
> on the local CPU), the simplified one below should be sufficient.

Rock solid, after this patch the issues are gone and system stable.
Using it as stabilizer base for all v4.2 work now.

Excellent work Rafael!

Tested-by: Linus Walleij <linus.walleij@...aro.org>

Yours,
Linus Walleij
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