Nick Piggin wrote:
Arjan van de Ven wrote:
Jesse Barnes wrote:
On Thursday, August 24, 2006 10:41 am, Arjan van de Ven wrote:
The reason for adding this infrastructure is that power management in
the idle loop needs to make a tradeoff between latency and power
savings (deeper power save modes have a longer latency to running code
again).
What if a processor was already in a sleep state when a call to
set_acceptable_latency() latency occurs?
there's nothing sane that can be done in that case; any wake up
already will cause the unwanted latency!
A premature wakeup is only making it happen *now*, but now is as
inconvenient a time as any...
(in fact it may be a worst case time scenario, say, an audio
interrupt...)
Surely you would call set_acceptable_latency() *before* running such
operation that requires the given latency? And that set_acceptable_latency
would block the caller until all CPUs are set to wake within this latency.
That would be the API semantics I would expect, anyway.
but that means it blocks, and thus can't be used in irq context
(the usage model I imagine happens most is a set_acceptable_latency() which can block during device init,
with either no or a very course limit, and a modify_acceptable_latency(), which cannot block, from irq context or
device open)
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