From: "H.J. Lu" <hjl.tools@gmail.com>
To: libc-alpha@sourceware.org
Cc: Florian Weimer <fweimer@redhat.com>,
Oleh Derevenko <oleh.derevenko@gmail.com>,
Arjan van de Ven <arjan@linux.intel.com>,
Andreas Schwab <schwab@linux-m68k.org>,
"Paul A . Clarke" <pc@us.ibm.com>,
Noah Goldstein <goldstein.w.n@gmail.com>
Subject: [PATCH v6 3/4] Reduce CAS in malloc spinlocks
Date: Thu, 11 Nov 2021 08:24:27 -0800 [thread overview]
Message-ID: <20211111162428.2286605-4-hjl.tools@gmail.com> (raw)
In-Reply-To: <20211111162428.2286605-1-hjl.tools@gmail.com>
Do an atomic load and check if compare may fail. Skip CAS and spin if
compare may fail to reduce cache line bouncing on contended locks.
---
malloc/arena.c | 5 +++++
malloc/malloc.c | 10 ++++++++++
2 files changed, 15 insertions(+)
diff --git a/malloc/arena.c b/malloc/arena.c
index 78ef4cf18c..e7fbe7c183 100644
--- a/malloc/arena.c
+++ b/malloc/arena.c
@@ -899,6 +899,11 @@ arena_get2 (size_t size, mstate avoid_arena)
enough address space to create that many arenas. */
if (__glibc_unlikely (n <= narenas_limit - 1))
{
+ if (atomic_load_relaxed (&narenas) != n)
+ {
+ atomic_spin_nop ();
+ goto repeat;
+ }
if (catomic_compare_and_exchange_bool_acq (&narenas, n + 1, n))
goto repeat;
a = _int_new_arena (size);
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 095d97a3be..403ffb84ef 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -3717,6 +3717,11 @@ _int_malloc (mstate av, size_t bytes)
pp = REVEAL_PTR (victim->fd); \
if (__glibc_unlikely (pp != NULL && misaligned_chunk (pp))) \
malloc_printerr ("malloc(): unaligned fastbin chunk detected"); \
+ if (atomic_load_relaxed (fb) != victim) \
+ { \
+ atomic_spin_nop (); \
+ continue; \
+ } \
} \
while ((pp = catomic_compare_and_exchange_val_acq (fb, pp, victim)) \
!= victim); \
@@ -4435,6 +4440,11 @@ _int_free (mstate av, mchunkptr p, int have_lock)
malloc_printerr ("double free or corruption (fasttop)");
old2 = old;
p->fd = PROTECT_PTR (&p->fd, old);
+ if (atomic_load_relaxed (fb) != old2)
+ {
+ atomic_spin_nop ();
+ continue;
+ }
}
while ((old = catomic_compare_and_exchange_val_rel (fb, p, old2))
!= old2);
--
2.33.1
next prev parent reply other threads:[~2021-11-11 16:24 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-11 16:24 [PATCH v6 0/4] Optimize CAS [BZ #28537] H.J. Lu
2021-11-11 16:24 ` [PATCH v6 1/4] Add LLL_MUTEX_READ_LOCK " H.J. Lu
2021-11-12 17:23 ` Szabolcs Nagy
2021-11-17 2:24 ` Noah Goldstein
2021-11-17 23:54 ` H.J. Lu
2021-11-18 0:03 ` Noah Goldstein
2021-11-18 0:31 ` H.J. Lu
2021-11-18 1:16 ` Arjan van de Ven
2022-09-11 20:19 ` Sunil Pandey
2022-09-29 0:10 ` Noah Goldstein
2021-11-11 16:24 ` [PATCH v6 2/4] Avoid extra load with CAS in __pthread_mutex_lock_full " H.J. Lu
2021-11-12 16:31 ` Szabolcs Nagy
2021-11-12 18:50 ` Andreas Schwab
2022-09-11 20:16 ` Sunil Pandey
2022-09-29 0:10 ` Noah Goldstein
2021-11-11 16:24 ` H.J. Lu [this message]
2023-02-23 5:48 ` [PATCH v6 3/4] Reduce CAS in malloc spinlocks DJ Delorie
2021-11-11 16:24 ` [PATCH v6 4/4] Avoid extra load with CAS in __pthread_mutex_clocklock_common [BZ #28537] H.J. Lu
2021-11-12 16:32 ` Szabolcs Nagy
2021-11-12 18:51 ` Andreas Schwab
2022-09-11 20:12 ` Sunil Pandey
2022-09-11 20:15 ` Arjan van de Ven
2022-09-11 21:26 ` Florian Weimer
2022-09-29 0:09 ` Noah Goldstein
2021-11-15 13:01 [PATCH v6 3/4] Reduce CAS in malloc spinlocks Wilco Dijkstra
2023-02-23 18:27 Wilco Dijkstra
2023-02-23 19:53 ` H.J. Lu
2023-02-23 20:07 ` DJ Delorie
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