From 837e72f78a72ef43a0c5e179f3addadb2a225f80 Mon Sep 17 00:00:00 2001 From: Nicholas Piggin Date: Fri, 9 Jun 2017 01:36:07 +1000 Subject: [PATCH] powerpc/64: Drop reservation-clearing ldarx in context switch There is no need to explicitly break the reservation in _switch, because we are guaranteed that the context switch path will include a larx/stcx. Comment the guarantee and remove the reservation clear from _switch. This is worth 1-2% in context switch performance. Signed-off-by: Nicholas Piggin Signed-off-by: Michael Ellerman --- arch/powerpc/kernel/entry_64.S | 11 +++-------- 1 file changed, 3 insertions(+), 8 deletions(-) diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index 91f9fdc2d027..273a35926534 100644 --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -521,15 +521,10 @@ _GLOBAL(_switch) #endif /* CONFIG_SMP */ /* - * If we optimise away the clear of the reservation in system - * calls because we know the CPU tracks the address of the - * reservation, then we need to clear it here to cover the - * case that the kernel context switch path has no larx - * instructions. + * The kernel context switch path must contain a spin_lock, + * which contains larx/stcx, which will clear any reservation + * of the task being switched. */ -BEGIN_FTR_SECTION - ldarx r6,0,r1 -END_FTR_SECTION_IFSET(CPU_FTR_STCX_CHECKS_ADDRESS) BEGIN_FTR_SECTION /* -- 2.11.0