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| author | Nicholas Piggin <npiggin@gmail.com> | 2017-06-09 01:36:07 +1000 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2017-06-15 16:34:39 +1000 |
| commit | 837e72f78a72ef43a0c5e179f3addadb2a225f80 (patch) | |
| tree | 4a16400f9dc5667da0e16a4ac9cbf9764773f21d /arch/powerpc/kernel/entry_64.S | |
| parent | e4c0fc5f72bca11432297168338aef46c12793a4 (diff) | |
| download | linux-837e72f78a72ef43a0c5e179f3addadb2a225f80.tar.gz | |
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 <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/kernel/entry_64.S')
| -rw-r--r-- | arch/powerpc/kernel/entry_64.S | 11 |
1 files 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 /* |