* [PATCH 1/2] x86/locking: Use ALT_OUTPUT_SP() for percpu_{,try_}cmpxchg{64,128}_op()
@ 2025-01-13 15:59 Uros Bizjak
2025-01-13 15:59 ` [PATCH 2/2] x86/locking: Use asm_inline for {,try_}cmpxchg{64,128} emulations Uros Bizjak
0 siblings, 1 reply; 2+ messages in thread
From: Uros Bizjak @ 2025-01-13 15:59 UTC (permalink / raw)
To: x86, linux-mm, linux-kernel
Cc: Uros Bizjak, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, H. Peter Anvin, Dennis Zhou, Tejun Heo,
Christoph Lameter, Peter Zijlstra (Intel)
percpu_{,try_}cmpxchg{64,128}() macros use CALL instruction inside
asm statement in one of their alternatives. Use ALT_OUTPUT_SP()
macro to add required dependence on %esp register.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
---
arch/x86/include/asm/percpu.h | 28 ++++++++++++++--------------
1 file changed, 14 insertions(+), 14 deletions(-)
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index e525cd85f999..0ab991fba7de 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -350,9 +350,9 @@ do { \
\
asm qual (ALTERNATIVE("call this_cpu_cmpxchg8b_emu", \
"cmpxchg8b " __percpu_arg([var]), X86_FEATURE_CX8) \
- : [var] "+m" (__my_cpu_var(_var)), \
- "+a" (old__.low), \
- "+d" (old__.high) \
+ : ALT_OUTPUT_SP([var] "+m" (__my_cpu_var(_var)), \
+ "+a" (old__.low), \
+ "+d" (old__.high)) \
: "b" (new__.low), \
"c" (new__.high), \
"S" (&(_var)) \
@@ -381,10 +381,10 @@ do { \
asm qual (ALTERNATIVE("call this_cpu_cmpxchg8b_emu", \
"cmpxchg8b " __percpu_arg([var]), X86_FEATURE_CX8) \
CC_SET(z) \
- : CC_OUT(z) (success), \
- [var] "+m" (__my_cpu_var(_var)), \
- "+a" (old__.low), \
- "+d" (old__.high) \
+ : ALT_OUTPUT_SP(CC_OUT(z) (success), \
+ [var] "+m" (__my_cpu_var(_var)), \
+ "+a" (old__.low), \
+ "+d" (old__.high)) \
: "b" (new__.low), \
"c" (new__.high), \
"S" (&(_var)) \
@@ -421,9 +421,9 @@ do { \
\
asm qual (ALTERNATIVE("call this_cpu_cmpxchg16b_emu", \
"cmpxchg16b " __percpu_arg([var]), X86_FEATURE_CX16) \
- : [var] "+m" (__my_cpu_var(_var)), \
- "+a" (old__.low), \
- "+d" (old__.high) \
+ : ALT_OUTPUT_SP([var] "+m" (__my_cpu_var(_var)), \
+ "+a" (old__.low), \
+ "+d" (old__.high)) \
: "b" (new__.low), \
"c" (new__.high), \
"S" (&(_var)) \
@@ -452,10 +452,10 @@ do { \
asm qual (ALTERNATIVE("call this_cpu_cmpxchg16b_emu", \
"cmpxchg16b " __percpu_arg([var]), X86_FEATURE_CX16) \
CC_SET(z) \
- : CC_OUT(z) (success), \
- [var] "+m" (__my_cpu_var(_var)), \
- "+a" (old__.low), \
- "+d" (old__.high) \
+ : ALT_OUTPUT_SP(CC_OUT(z) (success), \
+ [var] "+m" (__my_cpu_var(_var)), \
+ "+a" (old__.low), \
+ "+d" (old__.high)) \
: "b" (new__.low), \
"c" (new__.high), \
"S" (&(_var)) \
--
2.42.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* [PATCH 2/2] x86/locking: Use asm_inline for {,try_}cmpxchg{64,128} emulations
2025-01-13 15:59 [PATCH 1/2] x86/locking: Use ALT_OUTPUT_SP() for percpu_{,try_}cmpxchg{64,128}_op() Uros Bizjak
@ 2025-01-13 15:59 ` Uros Bizjak
0 siblings, 0 replies; 2+ messages in thread
From: Uros Bizjak @ 2025-01-13 15:59 UTC (permalink / raw)
To: x86, linux-mm, linux-kernel
Cc: Uros Bizjak, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, H. Peter Anvin, Dennis Zhou, Tejun Heo,
Christoph Lameter, Peter Zijlstra (Intel)
According to [1], the usage of asm pseudo directives in the asm template
can confuse the compiler to wrongly estimate the size of the generated
code. ALTERNATIVE macro expands to several asm pseudo directives, so
its usage in {,try_}cmpxchg{64,128} causes instruction length estimate
to fail by an order of magnitude (the compiler estimates the length of
an asm to be more than 20 instructions). This wrong estimate further
causes unoptimal inlining decisions for functions that use these
locking primitives.
Use asm_inline instead of just asm. For inlining purposes, the size of
the asm is then taken as the minimum size, ignoring how many instructions
compiler thinks it is.
[1] https://gcc.gnu.org/onlinedocs/gcc/Size-of-an-asm.html
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
---
arch/x86/include/asm/cmpxchg_32.h | 32 +++++++------
arch/x86/include/asm/percpu.h | 77 +++++++++++++++----------------
2 files changed, 55 insertions(+), 54 deletions(-)
diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h
index fd1282a783dd..95b5f990ca88 100644
--- a/arch/x86/include/asm/cmpxchg_32.h
+++ b/arch/x86/include/asm/cmpxchg_32.h
@@ -91,12 +91,14 @@ static __always_inline bool __try_cmpxchg64_local(volatile u64 *ptr, u64 *oldp,
union __u64_halves o = { .full = (_old), }, \
n = { .full = (_new), }; \
\
- asm volatile(ALTERNATIVE(_lock_loc \
- "call cmpxchg8b_emu", \
- _lock "cmpxchg8b %a[ptr]", X86_FEATURE_CX8) \
- : ALT_OUTPUT_SP("+a" (o.low), "+d" (o.high)) \
- : "b" (n.low), "c" (n.high), [ptr] "S" (_ptr) \
- : "memory"); \
+ asm_inline volatile( \
+ ALTERNATIVE(_lock_loc \
+ "call cmpxchg8b_emu", \
+ _lock "cmpxchg8b %a[ptr]", X86_FEATURE_CX8) \
+ : ALT_OUTPUT_SP("+a" (o.low), "+d" (o.high)) \
+ : "b" (n.low), "c" (n.high), \
+ [ptr] "S" (_ptr) \
+ : "memory"); \
\
o.full; \
})
@@ -119,14 +121,16 @@ static __always_inline u64 arch_cmpxchg64_local(volatile u64 *ptr, u64 old, u64
n = { .full = (_new), }; \
bool ret; \
\
- asm volatile(ALTERNATIVE(_lock_loc \
- "call cmpxchg8b_emu", \
- _lock "cmpxchg8b %a[ptr]", X86_FEATURE_CX8) \
- CC_SET(e) \
- : ALT_OUTPUT_SP(CC_OUT(e) (ret), \
- "+a" (o.low), "+d" (o.high)) \
- : "b" (n.low), "c" (n.high), [ptr] "S" (_ptr) \
- : "memory"); \
+ asm_inline volatile( \
+ ALTERNATIVE(_lock_loc \
+ "call cmpxchg8b_emu", \
+ _lock "cmpxchg8b %a[ptr]", X86_FEATURE_CX8) \
+ CC_SET(e) \
+ : ALT_OUTPUT_SP(CC_OUT(e) (ret), \
+ "+a" (o.low), "+d" (o.high)) \
+ : "b" (n.low), "c" (n.high), \
+ [ptr] "S" (_ptr) \
+ : "memory"); \
\
if (unlikely(!ret)) \
*(_oldp) = o.full; \
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 0ab991fba7de..08f5f61690b7 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -348,15 +348,14 @@ do { \
old__.var = _oval; \
new__.var = _nval; \
\
- asm qual (ALTERNATIVE("call this_cpu_cmpxchg8b_emu", \
- "cmpxchg8b " __percpu_arg([var]), X86_FEATURE_CX8) \
- : ALT_OUTPUT_SP([var] "+m" (__my_cpu_var(_var)), \
- "+a" (old__.low), \
- "+d" (old__.high)) \
- : "b" (new__.low), \
- "c" (new__.high), \
- "S" (&(_var)) \
- : "memory"); \
+ asm_inline qual ( \
+ ALTERNATIVE("call this_cpu_cmpxchg8b_emu", \
+ "cmpxchg8b " __percpu_arg([var]), X86_FEATURE_CX8) \
+ : ALT_OUTPUT_SP([var] "+m" (__my_cpu_var(_var)), \
+ "+a" (old__.low), "+d" (old__.high)) \
+ : "b" (new__.low), "c" (new__.high), \
+ "S" (&(_var)) \
+ : "memory"); \
\
old__.var; \
})
@@ -378,17 +377,16 @@ do { \
old__.var = *_oval; \
new__.var = _nval; \
\
- asm qual (ALTERNATIVE("call this_cpu_cmpxchg8b_emu", \
- "cmpxchg8b " __percpu_arg([var]), X86_FEATURE_CX8) \
- CC_SET(z) \
- : ALT_OUTPUT_SP(CC_OUT(z) (success), \
- [var] "+m" (__my_cpu_var(_var)), \
- "+a" (old__.low), \
- "+d" (old__.high)) \
- : "b" (new__.low), \
- "c" (new__.high), \
- "S" (&(_var)) \
- : "memory"); \
+ asm_inline qual ( \
+ ALTERNATIVE("call this_cpu_cmpxchg8b_emu", \
+ "cmpxchg8b " __percpu_arg([var]), X86_FEATURE_CX8) \
+ CC_SET(z) \
+ : ALT_OUTPUT_SP(CC_OUT(z) (success), \
+ [var] "+m" (__my_cpu_var(_var)), \
+ "+a" (old__.low), "+d" (old__.high)) \
+ : "b" (new__.low), "c" (new__.high), \
+ "S" (&(_var)) \
+ : "memory"); \
if (unlikely(!success)) \
*_oval = old__.var; \
\
@@ -419,15 +417,14 @@ do { \
old__.var = _oval; \
new__.var = _nval; \
\
- asm qual (ALTERNATIVE("call this_cpu_cmpxchg16b_emu", \
- "cmpxchg16b " __percpu_arg([var]), X86_FEATURE_CX16) \
- : ALT_OUTPUT_SP([var] "+m" (__my_cpu_var(_var)), \
- "+a" (old__.low), \
- "+d" (old__.high)) \
- : "b" (new__.low), \
- "c" (new__.high), \
- "S" (&(_var)) \
- : "memory"); \
+ asm_inline qual ( \
+ ALTERNATIVE("call this_cpu_cmpxchg16b_emu", \
+ "cmpxchg16b " __percpu_arg([var]), X86_FEATURE_CX16) \
+ : ALT_OUTPUT_SP([var] "+m" (__my_cpu_var(_var)), \
+ "+a" (old__.low), "+d" (old__.high)) \
+ : "b" (new__.low), "c" (new__.high), \
+ "S" (&(_var)) \
+ : "memory"); \
\
old__.var; \
})
@@ -449,19 +446,19 @@ do { \
old__.var = *_oval; \
new__.var = _nval; \
\
- asm qual (ALTERNATIVE("call this_cpu_cmpxchg16b_emu", \
- "cmpxchg16b " __percpu_arg([var]), X86_FEATURE_CX16) \
- CC_SET(z) \
- : ALT_OUTPUT_SP(CC_OUT(z) (success), \
- [var] "+m" (__my_cpu_var(_var)), \
- "+a" (old__.low), \
- "+d" (old__.high)) \
- : "b" (new__.low), \
- "c" (new__.high), \
- "S" (&(_var)) \
- : "memory"); \
+ asm_inline qual ( \
+ ALTERNATIVE("call this_cpu_cmpxchg16b_emu", \
+ "cmpxchg16b " __percpu_arg([var]), X86_FEATURE_CX16) \
+ CC_SET(z) \
+ : ALT_OUTPUT_SP(CC_OUT(z) (success), \
+ [var] "+m" (__my_cpu_var(_var)), \
+ "+a" (old__.low), "+d" (old__.high)) \
+ : "b" (new__.low), "c" (new__.high), \
+ "S" (&(_var)) \
+ : "memory"); \
if (unlikely(!success)) \
*_oval = old__.var; \
+ \
likely(success); \
})
--
2.42.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
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2025-01-13 15:59 ` [PATCH 2/2] x86/locking: Use asm_inline for {,try_}cmpxchg{64,128} emulations Uros Bizjak
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