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From: Wilco Dijkstra <wilco@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc] libio: Improve performance of IO locks Date: Thu, 11 Aug 2022 16:28:56 +0000 (GMT) [thread overview] Message-ID: <20220811162856.630773858C74@sourceware.org> (raw) 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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