From: Florian Weimer <fweimer@redhat.com>
To: libc-alpha@sourceware.org
Subject: [PATCH] nptl: Use out-of-line wake function in __libc_lock_unlock slow path
Date: Wed, 07 Jul 2021 16:52:29 +0200 [thread overview]
Message-ID: <87lf6i5g7m.fsf@oldenburg.str.redhat.com> (raw)
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
---
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)
next reply other threads:[~2021-07-07 14:52 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-07 14:52 Florian Weimer [this message]
2021-07-08 18:17 ` Adhemerval Zanella
2021-07-08 18:24 ` Florian Weimer
2021-07-08 18:27 ` Adhemerval Zanella
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87lf6i5g7m.fsf@oldenburg.str.redhat.com \
--to=fweimer@redhat.com \
--cc=libc-alpha@sourceware.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).