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Anton Blanchard 152d523e63 powerpc: Create context switch helpers save_sprs() and restore_sprs()

Move all our context switch SPR save and restore code into two
helpers. We do a few optimisations:

- Group all mfsprs and all mtsprs. In many cases an mtspr sets a
scoreboarding bit that an mfspr waits on, so the current practise of
mfspr A; mtspr A; mfpsr B; mtspr B is the worst scheduling we can
do.

- SPR writes are slow, so check that the value is changing before
writing it.

A context switch microbenchmark using yield():

http://ozlabs.org/~anton/junkcode/context_switch2.c

./context_switch2 --test=yield 0 0

shows an improvement of almost 10% on POWER8.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

2015-12-01 13:52:24 +11:00

alpha

…

arc

ARC fixes for 4.4-rc1

2015-11-14 09:09:37 -08:00

arm

USB fixes for 4.4-rc2

2015-11-22 13:15:05 -08:00

arm64

arm64 fixes:

2015-11-19 12:21:23 -08:00