Sounds good, tested on x86_64.
On Mon, Aug 1, 2022 at 7:06 AM Wilco Dijkstra via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
>
> ping
>
>
> 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
> 2.9 times. Multithreaded performance improved by 2%.
>
> Passes GLIBC testsuite, OK for commit?
>
> ---
>
> diff --git a/sysdeps/nptl/stdio-lock.h b/sysdeps/nptl/stdio-lock.h
> index afa0b779c81d7dd915f8edb6c0974e4f231d4e0a..45823cd1629d3e3efecc64a7d07706a6e6de9af1 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)
>
>