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Message-Id: <20190613135653.623354057@infradead.org>
Date: Thu, 13 Jun 2019 15:54:50 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: torvalds@...ux-foundation.org, mingo@...nel.org, bp@...en8.de,
tglx@...utronix.de, luto@...nel.org, namit@...are.com,
peterz@...radead.org
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH v2 5/5] x86/percpu: Optimize raw_cpu_xchg()
Since raw_cpu_xchg() doesn't need to be IRQ-safe, like
this_cpu_xchg(), we can use a simple load-store instead of the cmpxchg
loop.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
arch/x86/include/asm/percpu.h | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -407,9 +407,21 @@ do { \
#define raw_cpu_or_1(pcp, val) percpu_to_op(, "or", (pcp), val)
#define raw_cpu_or_2(pcp, val) percpu_to_op(, "or", (pcp), val)
#define raw_cpu_or_4(pcp, val) percpu_to_op(, "or", (pcp), val)
-#define raw_cpu_xchg_1(pcp, val) percpu_xchg_op(, pcp, val)
-#define raw_cpu_xchg_2(pcp, val) percpu_xchg_op(, pcp, val)
-#define raw_cpu_xchg_4(pcp, val) percpu_xchg_op(, pcp, val)
+
+/*
+ * raw_cpu_xchg() can use a load-store since it is not required to be
+ * IRQ-safe.
+ */
+#define raw_percpu_xchg_op(var, nval) \
+({ \
+ typeof(var) pxo_ret__ = raw_cpu_read(var); \
+ raw_cpu_write(var, (nval)); \
+ pxo_ret__; \
+})
+
+#define raw_cpu_xchg_1(pcp, val) raw_percpu_xchg_op(pcp, val)
+#define raw_cpu_xchg_2(pcp, val) raw_percpu_xchg_op(pcp, val)
+#define raw_cpu_xchg_4(pcp, val) raw_percpu_xchg_op(pcp, val)
#define this_cpu_read_1(pcp) percpu_from_op(volatile, "mov", pcp)
#define this_cpu_read_2(pcp) percpu_from_op(volatile, "mov", pcp)
@@ -472,7 +484,7 @@ do { \
#define raw_cpu_and_8(pcp, val) percpu_to_op(, "and", (pcp), val)
#define raw_cpu_or_8(pcp, val) percpu_to_op(, "or", (pcp), val)
#define raw_cpu_add_return_8(pcp, val) percpu_add_return_op(, pcp, val)
-#define raw_cpu_xchg_8(pcp, nval) percpu_xchg_op(, pcp, nval)
+#define raw_cpu_xchg_8(pcp, nval) raw_percpu_xchg_op(pcp, nval)
#define raw_cpu_cmpxchg_8(pcp, oval, nval) percpu_cmpxchg_op(, pcp, oval, nval)
#define this_cpu_read_8(pcp) percpu_from_op(volatile, "mov", pcp)
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