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bc4f65e4cf
The syscall exit code that branches to restore_math is quite heavy on Book3S, consisting of 2 mtmsr instructions. Threads that don't use both FP and vector can get caught here if the kernel ever uses FP or vector. Lazy-FP/vec context switching also trips this case. So check for lazy FP and vector before switching RI for restore_math. Move most of this case out of line. For threads that do want to restore math registers, the MSR switches are still suboptimal. Future direction may be to use a soft-RI bit to avoid MSR switches in kernel (similar to soft-EE), but for now at least the no-restore POWER9 context switch rate increases by about 5% due to sched_yield(2) return performance. I haven't constructed a test to measure the syscall cost. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> |
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boot | ||
configs | ||
crypto | ||
include | ||
kernel | ||
kvm | ||
lib | ||
math-emu | ||
mm | ||
net | ||
oprofile | ||
perf | ||
platforms | ||
purgatory | ||
sysdev | ||
tools | ||
xmon | ||
Kconfig | ||
Kconfig.debug | ||
Makefile | ||
Makefile.postlink |