From d779c07dd72098a7416d907494f958213b7726f3 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Thu, 27 Jun 2013 12:01:51 +0100 Subject: [PATCH] ARM: bitops: prefetch the destination word for write prior to strex The cost of changing a cacheline from shared to exclusive state can be significant, especially when this is triggered by an exclusive store, since it may result in having to retry the transaction. This patch prefixes our atomic bitops implementation with prefetchw, to try and grab the line in exclusive state from the start. The testop macro is left alone, since the barrier semantics limit the usefulness of prefetching data. Acked-by: Nicolas Pitre Signed-off-by: Will Deacon --- arch/arm/lib/bitops.h | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/arm/lib/bitops.h b/arch/arm/lib/bitops.h index d6408d1ee543..e0c68d5bb7dc 100644 --- a/arch/arm/lib/bitops.h +++ b/arch/arm/lib/bitops.h @@ -10,6 +10,11 @@ UNWIND( .fnstart ) and r3, r0, #31 @ Get bit offset mov r0, r0, lsr #5 add r1, r1, r0, lsl #2 @ Get word offset +#if __LINUX_ARM_ARCH__ >= 7 + .arch_extension mp + ALT_SMP(W(pldw) [r1]) + ALT_UP(W(nop)) +#endif mov r3, r2, lsl r3 1: ldrex r2, [r1] \instr r2, r2, r3