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locks: take the number of readers into account when waiting

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Previous code would always spin once before checking the lock. But a lock
with e.g. 6 readers is not going to become free in the duration of once spin
even if they start draining immediately.

Conservatively perform one for each reader.

Note that the total number of allowed spins is still extremely small and is
subject to change later.

MFC after:	1 week
This commit is contained in:
mjg 2017-10-05 19:18:02 +00:00
parent c2dbc3a78e
commit 6f516b023d
3 changed files with 19 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
sys/kern/kern_rwlock.c
View File

@ -414,7 +414,7 @@ __rw_rlock_hard(volatile uintptr_t *c, struct thread *td, uintptr_t v,
#ifdef ADAPTIVE_RWLOCKS
volatile struct thread *owner;
int spintries = 0;
int i;
int i, n;
#endif
#ifdef LOCK_PROFILING
uint64_t waittime = 0;
@ -488,8 +488,9 @@ __rw_rlock_hard(volatile uintptr_t *c, struct thread *td, uintptr_t v,
KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
"spinning", "lockname:\"%s\"",
rw->lock_object.lo_name);
for (i = 0; i < rowner_loops; i++) {
cpu_spinwait();
for (i = 0; i < rowner_loops; i += n) {
n = RW_READERS(v);
lock_delay_spin(n);
v = RW_READ_VALUE(rw);
if ((v & RW_LOCK_READ) == 0 || RW_CAN_READ(td, v))
break;
@ -830,7 +831,7 @@ __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v, uintptr_t tid,
#ifdef ADAPTIVE_RWLOCKS
volatile struct thread *owner;
int spintries = 0;
int i;
int i, n;
#endif
uintptr_t x;
#ifdef LOCK_PROFILING
@ -928,8 +929,9 @@ __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v, uintptr_t tid,
KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
"spinning", "lockname:\"%s\"",
rw->lock_object.lo_name);
for (i = 0; i < rowner_loops; i++) {
cpu_spinwait();
for (i = 0; i < rowner_loops; i += n) {
n = RW_READERS(v);
lock_delay_spin(n);
v = RW_READ_VALUE(rw);
if ((v & RW_LOCK_WRITE_SPINNER) == 0)
break;

7
sys/kern/kern_sx.c
View File

@ -502,7 +502,7 @@ _sx_xlock_hard(struct sx *sx, uintptr_t x, uintptr_t tid, int opts,
GIANT_DECLARE;
#ifdef ADAPTIVE_SX
volatile struct thread *owner;
u_int i, spintries = 0;
u_int i, n, spintries = 0;
#endif
#ifdef LOCK_PROFILING
uint64_t waittime = 0;
@ -600,12 +600,13 @@ _sx_xlock_hard(struct sx *sx, uintptr_t x, uintptr_t tid, int opts,
"lockname:\"%s\"", sx->lock_object.lo_name);
GIANT_SAVE();
spintries++;
for (i = 0; i < asx_loops; i++) {
for (i = 0; i < asx_loops; i += n) {
if (LOCK_LOG_TEST(&sx->lock_object, 0))
CTR4(KTR_LOCK,
"%s: shared spinning on %p with %u and %u",
__func__, sx, spintries, i);
cpu_spinwait();
n = SX_SHARERS(x);
lock_delay_spin(n);
x = SX_READ_VALUE(sx);
if ((x & SX_LOCK_SHARED) == 0 ||
SX_SHARERS(x) == 0)

7
sys/sys/lock.h
View File

@ -226,6 +226,13 @@ lock_delay_arg_init(struct lock_delay_arg *la, struct lock_delay_config *lc)
la->spin_cnt = 0;
}
#define lock_delay_spin(n) do { \
u_int _i; \
\
for (_i = (n); _i > 0; _i--) \
cpu_spinwait(); \
} while (0)
#define LOCK_DELAY_SYSINIT(func) \
SYSINIT(func##_ld, SI_SUB_LOCK, SI_ORDER_ANY, func, NULL)