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From: Florian Weimer <fw@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc] nptl: Use out-of-line wake function in __libc_lock_unlock slow path Date: Fri, 9 Jul 2021 09:06:23 +0000 (GMT) [thread overview] Message-ID: <20210709090623.7C0C938515FF@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=508ee037a30f1d4f6a1f8de2bd0d9866d4684625 commit 508ee037a30f1d4f6a1f8de2bd0d9866d4684625 Author: Florian Weimer <fweimer@redhat.com> Date: Fri Jul 9 10:59:22 2021 +0200 nptl: Use out-of-line wake function in __libc_lock_unlock slow path This slightly reduces code size, as can be seen below. __libc_lock_unlock is usually used along with __libc_lock_lock in the same function. __libc_lock_lock already has an out-of-line slow path, so this change should not introduce many additional non-leaf functions. This change also fixes a link failure in 32-bit Arm thumb mode because commit 1f9c804fbd699104adefbce9e56d2c8aa711b6b9 ("nptl: Use internal low-level lock type for !IS_IN (libc)") introduced __libc_do_syscall calls outside of libc. Before x86-64: text data bss dec hex filename 1937748 20456 54896 2013100 1eb7ac libc.so.6 25601 856 12768 39225 9939 nss/libnss_db.so.2 40310 952 25144 66406 10366 nss/libnss_files.so.2 After x86-64: text data bss dec hex filename 1935312 20456 54896 2010664 1eae28 libc.so.6 25559 864 12768 39191 9917 nss/libnss_db.so.2 39764 960 25144 65868 1014c nss/libnss_files.so.2 Before i686: 2110961 11272 39144 2161377 20fae1 libc.so.6 27243 428 12652 40323 9d83 nss/libnss_db.so.2 43062 476 25028 68566 10bd6 nss/libnss_files.so.2 After i686: 2107347 11272 39144 2157763 20ecc3 libc.so.6 26929 432 12652 40013 9c4d nss/libnss_db.so.2 43132 480 25028 68640 10c20 nss/libnss_files.so.2 Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> Diff: --- nptl/Versions | 1 + nptl/lowlevellock.c | 14 ++++++++++++++ sysdeps/nptl/lowlevellock.h | 26 ++++++++++++++++++-------- 3 files changed, 33 insertions(+), 8 deletions(-) diff --git a/nptl/Versions b/nptl/Versions index 2a75f013f2..3221de89d1 100644 --- a/nptl/Versions +++ b/nptl/Versions @@ -380,6 +380,7 @@ libc { } GLIBC_PRIVATE { __libc_alloca_cutoff; + __lll_lock_wake_private; __lll_lock_wait_private; __nptl_create_event; __nptl_death_event; diff --git a/nptl/lowlevellock.c b/nptl/lowlevellock.c index 2d077d8694..4f88178964 100644 --- a/nptl/lowlevellock.c +++ b/nptl/lowlevellock.c @@ -52,6 +52,20 @@ __lll_lock_wait (int *futex, int private) } libc_hidden_def (__lll_lock_wait) +void +__lll_lock_wake_private (int *futex) +{ + lll_futex_wake (futex, 1, LLL_PRIVATE); +} +libc_hidden_def (__lll_lock_wake_private) + +void +__lll_lock_wake (int *futex, int private) +{ + lll_futex_wake (futex, 1, private); +} +libc_hidden_def (__lll_lock_wake) + #if ENABLE_ELISION_SUPPORT int __pthread_force_elision __attribute__ ((nocommon)); libc_hidden_data_def (__pthread_force_elision) diff --git a/sysdeps/nptl/lowlevellock.h b/sysdeps/nptl/lowlevellock.h index be60c9ac28..4d95114ed3 100644 --- a/sysdeps/nptl/lowlevellock.h +++ b/sysdeps/nptl/lowlevellock.h @@ -125,6 +125,11 @@ libc_hidden_proto (__lll_lock_wait) #define lll_cond_lock(futex, private) __lll_cond_lock (&(futex), private) +extern void __lll_lock_wake_private (int *futex); +libc_hidden_proto (__lll_lock_wake_private) +extern void __lll_lock_wake (int *futex, int private); +libc_hidden_proto (__lll_lock_wake) + /* This is an expression rather than a statement even though its value is void, so that it can be used in a comma expression or as an expression that's cast to void. */ @@ -137,14 +142,19 @@ libc_hidden_proto (__lll_lock_wait) acquires the lock and when there will be no further lock acquisitions; thus, we must not access the lock after releasing it, or those accesses could be concurrent with mutex destruction or reuse of the memory. */ -#define __lll_unlock(futex, private) \ - ((void) \ - ({ \ - int *__futex = (futex); \ - int __private = (private); \ - int __oldval = atomic_exchange_rel (__futex, 0); \ - if (__glibc_unlikely (__oldval > 1)) \ - lll_futex_wake (__futex, 1, __private); \ +#define __lll_unlock(futex, private) \ + ((void) \ + ({ \ + int *__futex = (futex); \ + int __private = (private); \ + int __oldval = atomic_exchange_rel (__futex, 0); \ + if (__glibc_unlikely (__oldval > 1)) \ + { \ + if (__builtin_constant_p (private) && (private) == LLL_PRIVATE) \ + __lll_lock_wake_private (__futex); \ + else \ + __lll_lock_wake (__futex, __private); \ + } \ })) #define lll_unlock(futex, private) \ __lll_unlock (&(futex), private)
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