The current delay implementation uses the yield instruction, which is a
hint that it is beneficial to schedule another thread. As this is a hint,
it may be implemented as a NOP, causing all delays to be busy loops. This
is the case for many existing CPUs.
Taking advantage of the generic timer sending periodic events to all
cores, we can use WFE during delays to reduce power consumption. This is
beneficial only for delays longer than the period of the timer event
stream.
If timer event stream is not enabled, delays will behave as yield/busy
loops.
Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
(cherry picked from commit 39fac4930753aef801fca49043b6fe30a1179137)
(cherry picked from commit dc10a84ee56061793b2d41941a7a00b739aad150)
(cherry picked from commit 333b09c528dbace0b02ba73882cae9d6844061e5)
3fa3ec0300