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

From: Sudeep Holla
Date: Wed Apr 29 2015 - 05:51:08 EST

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@xxxxxxx>

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