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

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Message-ID: <5540A981.6060209@arm.com>
Date:	Wed, 29 Apr 2015 10:50:57 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Sudeep Holla <sudeep.holla@....com>,
	Linus Walleij <linus.walleij@...aro.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

Hi Rafael,

On 29/04/15 02:04, Rafael J. Wysocki 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.
>

Tested-by: Sudeep Holla <sudeep.holla@....com>

Regards,
Sudeep
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