powerpc/64s: Idle POWER8 avoid full state loss recovery where possible
If not all threads were in winkle, full state loss recovery is not necessary and can be avoided. A previous patch removed this optimisation due to some complexity with the implementation. Re-implement it by counting the number of threads in winkle with the per-core idle state. Only restore full state loss if all threads were in winkle. This has a small window of false positives right before threads execute winkle and just after they wake up, when the winkle count does not reflect the true number of threads in winkle. This is not a significant problem in comparison with even the minimum winkle duration. For correctness, a false positive is not a problem (only false negatives would be). Reviewed-by:Gautham R. Shenoy <ego@linux.vnet.ibm.com> Signed-off-by:
Nicholas Piggin <npiggin@gmail.com> Signed-off-by:
Michael Ellerman <mpe@ellerman.id.au>
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e420249d
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