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@@ -1,90 +0,0 @@
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-From 8d81ba8c0bc6fe31136cb15c9c82ef4c24965040 Mon Sep 17 00:00:00 2001
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-From: Rich Felker <[email protected]>
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-Date: Fri, 22 May 2020 17:45:47 -0400
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-Subject: [PATCH 4/4] restore lock-skipping for processes that return to
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- single-threaded state
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-
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-the design used here relies on the barrier provided by the first lock
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-operation after the process returns to single-threaded state to
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-synchronize with actions by the last thread that exited. by storing
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-the intent to change modes in the same object used to detect whether
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-locking is needed, it's possible to avoid an extra (possibly costly)
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-memory load after the lock is taken.
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----
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- src/internal/libc.h | 1 +
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- src/malloc/malloc.c | 5 ++++-
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- src/thread/__lock.c | 4 +++-
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- src/thread/pthread_create.c | 8 ++++----
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- 4 files changed, 12 insertions(+), 6 deletions(-)
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-
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---- a/src/internal/libc.h
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-+++ b/src/internal/libc.h
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-@@ -21,6 +21,7 @@ struct __libc {
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- char can_do_threads;
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- char threaded;
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- char secure;
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-+ volatile signed char need_locks;
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- int threads_minus_1;
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- size_t *auxv;
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- struct tls_module *tls_head;
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---- a/src/malloc/malloc.c
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-+++ b/src/malloc/malloc.c
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-@@ -26,8 +26,11 @@ int __malloc_replaced;
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-
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- static inline void lock(volatile int *lk)
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- {
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-- if (libc.threaded)
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-+ int need_locks = libc.need_locks;
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-+ if (need_locks) {
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- while(a_swap(lk, 1)) __wait(lk, lk+1, 1, 1);
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-+ if (need_locks < 0) libc.need_locks = 0;
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-+ }
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- }
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-
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- static inline void unlock(volatile int *lk)
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---- a/src/thread/__lock.c
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-+++ b/src/thread/__lock.c
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-@@ -18,9 +18,11 @@
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-
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- void __lock(volatile int *l)
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- {
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-- if (!libc.threaded) return;
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-+ int need_locks = libc.need_locks;
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-+ if (!need_locks) return;
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- /* fast path: INT_MIN for the lock, +1 for the congestion */
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- int current = a_cas(l, 0, INT_MIN + 1);
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-+ if (need_locks < 0) libc.need_locks = 0;
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- if (!current) return;
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- /* A first spin loop, for medium congestion. */
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- for (unsigned i = 0; i < 10; ++i) {
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---- a/src/thread/pthread_create.c
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-+++ b/src/thread/pthread_create.c
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-@@ -118,8 +118,8 @@ _Noreturn void __pthread_exit(void *resu
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- * until the lock is released, which only happens after SYS_exit
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- * has been called, via the exit futex address pointing at the lock.
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- * This needs to happen after any possible calls to LOCK() that might
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-- * skip locking if libc.threads_minus_1 is zero. */
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-- libc.threads_minus_1--;
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-+ * skip locking if process appears single-threaded. */
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-+ if (!--libc.threads_minus_1) libc.need_locks = -1;
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- self->next->prev = self->prev;
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- self->prev->next = self->next;
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- self->prev = self->next = self;
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-@@ -339,7 +339,7 @@ int __pthread_create(pthread_t *restrict
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- ~(1UL<<((SIGCANCEL-1)%(8*sizeof(long))));
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-
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- __tl_lock();
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-- libc.threads_minus_1++;
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-+ if (!libc.threads_minus_1++) libc.need_locks = 1;
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- ret = __clone((c11 ? start_c11 : start), stack, flags, args, &new->tid, TP_ADJ(new), &__thread_list_lock);
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-
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- /* All clone failures translate to EAGAIN. If explicit scheduling
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-@@ -363,7 +363,7 @@ int __pthread_create(pthread_t *restrict
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- new->next->prev = new;
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- new->prev->next = new;
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- } else {
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-- libc.threads_minus_1--;
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-+ if (!--libc.threads_minus_1) libc.need_locks = 0;
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- }
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- __tl_unlock();
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- __restore_sigs(&set);
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