Moving the wait loop for congested loops to its own function allows
us to add things to that wait loop, without growing the size of the
kernel text appreciably.
Signed-off-by: Rik van Riel <r...@redhat.com>
Reviewed-by: Steven Rostedt <rost...@goodmiss.org>
Reviewed-by: Michel Lespinasse <wal...@google.com>
Reviewed-by: Rafael Aquini <aqu...@redhat.com>
---
v2: clean up the code a little, after Michel's suggestion
arch/x86/include/asm/spinlock.h | 11 +++++------
arch/x86/kernel/smp.c | 14 ++++++++++++++
2 files changed, 19 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 33692ea..dc492f6 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -34,6 +34,8 @@
# define UNLOCK_LOCK_PREFIX
#endif
+extern void ticket_spin_lock_wait(arch_spinlock_t *, struct __raw_tickets);
+
/*
* Ticket locks are conceptually two parts, one indicating the current head of
* the queue, and the other indicating the current tail. The lock is acquired
@@ -53,12 +55,9 @@ static __always_inline void
__ticket_spin_lock(arch_spinlock_t *lock)
inc = xadd(&lock->tickets, inc);
- for (;;) {
- if (inc.head == inc.tail)
- break;
- cpu_relax();
- inc.head = ACCESS_ONCE(lock->tickets.head);
- }
+ if (inc.head != inc.tail)
+ ticket_spin_lock_wait(lock, inc);
+
barrier(); /* make sure nothing creeps before the lock is
taken */
}
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 48d2b7d..20da354 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -113,6 +113,20 @@ static atomic_t stopping_cpu = ATOMIC_INIT(-1);
static bool smp_no_nmi_ipi = false;
/*
+ * Wait on a congested ticket spinlock.
+ */
+void ticket_spin_lock_wait(arch_spinlock_t *lock, struct __raw_tickets inc)
+{
+ for (;;) {
+ cpu_relax();
+ inc.head = ACCESS_ONCE(lock->tickets.head);
+
+ if (inc.head == inc.tail)
+ break;
+ }
+}
+
+/*
* this function sends a 'reschedule' IPI to another CPU.
* it goes straight through and wastes no time serializing
* anything. Worst case is that we lose a reschedule ...
--
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