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* [glibc] libio: Improve performance of IO locks
@ 2022-08-11 16:28 Wilco Dijkstra
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From: Wilco Dijkstra @ 2022-08-11 16:28 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=c51c483d2b8ae66fe31a12509aedae02a6982ced
commit c51c483d2b8ae66fe31a12509aedae02a6982ced
Author: Wilco Dijkstra <wdijkstr@arm.com>
Date: Thu Aug 11 16:47:45 2022 +0100
libio: Improve performance of IO locks
Improve performance of recursive IO locks by adding a fast path for
the single-threaded case. To reduce the number of memory accesses for
locking/unlocking, only increment the recursion counter if the lock
is already taken.
On Neoverse V1, a microbenchmark with many small freads improved by
2.9x. Multithreaded performance improved by 2%.
Reviewed-by: Cristian Rodríguez <crrodriguez@opensuse.org>
Diff:
---
sysdeps/nptl/stdio-lock.h | 28 +++++++++++++++++++---------
1 file changed, 19 insertions(+), 9 deletions(-)
diff --git a/sysdeps/nptl/stdio-lock.h b/sysdeps/nptl/stdio-lock.h
index afa0b779c8..45823cd162 100644
--- a/sysdeps/nptl/stdio-lock.h
+++ b/sysdeps/nptl/stdio-lock.h
@@ -37,12 +37,18 @@ typedef struct { int lock; int cnt; void *owner; } _IO_lock_t;
#define _IO_lock_lock(_name) \
do { \
void *__self = THREAD_SELF; \
- if ((_name).owner != __self) \
+ if (SINGLE_THREAD_P && (_name).owner == NULL) \
+ { \
+ (_name).lock = LLL_LOCK_INITIALIZER_LOCKED; \
+ (_name).owner = __self; \
+ } \
+ else if ((_name).owner != __self) \
{ \
lll_lock ((_name).lock, LLL_PRIVATE); \
- (_name).owner = __self; \
+ (_name).owner = __self; \
} \
- ++(_name).cnt; \
+ else \
+ ++(_name).cnt; \
} while (0)
#define _IO_lock_trylock(_name) \
@@ -52,10 +58,7 @@ typedef struct { int lock; int cnt; void *owner; } _IO_lock_t;
if ((_name).owner != __self) \
{ \
if (lll_trylock ((_name).lock) == 0) \
- { \
- (_name).owner = __self; \
- (_name).cnt = 1; \
- } \
+ (_name).owner = __self; \
else \
__result = EBUSY; \
} \
@@ -66,11 +69,18 @@ typedef struct { int lock; int cnt; void *owner; } _IO_lock_t;
#define _IO_lock_unlock(_name) \
do { \
- if (--(_name).cnt == 0) \
+ if (SINGLE_THREAD_P && (_name).cnt == 0) \
+ { \
+ (_name).owner = NULL; \
+ (_name).lock = 0; \
+ } \
+ else if ((_name).cnt == 0) \
{ \
- (_name).owner = NULL; \
+ (_name).owner = NULL; \
lll_unlock ((_name).lock, LLL_PRIVATE); \
} \
+ else \
+ --(_name).cnt; \
} while (0)
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