5008 lock contention (rrw_exit) while running a read only load
Reviewed by: Matthew Ahrens <matthew.ahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Alex Reece <alex.reece@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: Richard Yao <ryao@gentoo.org>
Reviewed by: Saso Kiselkov <skiselkov.ml@gmail.com>
Approved by: Garrett D'Amore <garrett@damore.org>
Porting notes:
This patch ported perfectly cleanly to ZoL. During testing 100% cached
small-block reads, extreme contention was noticed on rrl->rr_lock from
rrw_exit() due to the frequent entering and leaving ZPL. Illumos picked
up this patch from FreeBSD and it also helps under Linux.
On a 1-minute 4K cached read test with 10 fio processes pinned to a single
socket on a 4-socket (10 thread per socket) NUMA system, contentions on
rrl->rr_lock were reduced from 508799 to 43085.
Ported-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #3555
#define RRW_LOCK_HELD(x) \
(rrw_held(x, RW_WRITER) || rrw_held(x, RW_READER))
+/*
+ * A reader-mostly lock implementation, tuning above reader-writer locks
+ * for hightly parallel read acquisitions, pessimizing write acquisitions.
+ *
+ * This should be a prime number. See comment in rrwlock.c near
+ * RRM_TD_LOCK() for details.
+ */
+#define RRM_NUM_LOCKS 17
+typedef struct rrmlock {
+ rrwlock_t locks[RRM_NUM_LOCKS];
+} rrmlock_t;
+
+void rrm_init(rrmlock_t *rrl, boolean_t track_all);
+void rrm_destroy(rrmlock_t *rrl);
+void rrm_enter(rrmlock_t *rrl, krw_t rw, void *tag);
+void rrm_enter_read(rrmlock_t *rrl, void *tag);
+void rrm_enter_write(rrmlock_t *rrl);
+void rrm_exit(rrmlock_t *rrl, void *tag);
+boolean_t rrm_held(rrmlock_t *rrl, krw_t rw);
+
+#define RRM_READ_HELD(x) rrm_held(x, RW_READER)
+#define RRM_WRITE_HELD(x) rrm_held(x, RW_WRITER)
+#define RRM_LOCK_HELD(x) \
+ (rrm_held(x, RW_WRITER) || rrm_held(x, RW_READER))
+
#ifdef __cplusplus
}
#endif
boolean_t z_atime; /* enable atimes mount option */
boolean_t z_relatime; /* enable relatime mount option */
boolean_t z_unmounted; /* unmounted */
- rrwlock_t z_teardown_lock;
+ rrmlock_t z_teardown_lock;
krwlock_t z_teardown_inactive_lock;
list_t z_all_znodes; /* all znodes in the fs */
uint64_t z_nr_znodes; /* number of znodes in the fs */
/* Called on entry to each ZFS vnode and vfs operation */
#define ZFS_ENTER(zsb) \
{ \
- rrw_enter_read(&(zsb)->z_teardown_lock, FTAG); \
+ rrm_enter_read(&(zsb)->z_teardown_lock, FTAG); \
if ((zsb)->z_unmounted) { \
ZFS_EXIT(zsb); \
return (EIO); \
/* Must be called before exiting the vop */
#define ZFS_EXIT(zsb) \
{ \
- rrw_exit(&(zsb)->z_teardown_lock, FTAG); \
+ rrm_exit(&(zsb)->z_teardown_lock, FTAG); \
}
/* Verifies the znode is valid */
(void *)curthread, (void *)rn->rn_rrl);
}
}
+
+/*
+ * A reader-mostly lock implementation, tuning above reader-writer locks
+ * for hightly parallel read acquisitions, while pessimizing writes.
+ *
+ * The idea is to split single busy lock into array of locks, so that
+ * each reader can lock only one of them for read, depending on result
+ * of simple hash function. That proportionally reduces lock congestion.
+ * Writer same time has to sequentially aquire write on all the locks.
+ * That makes write aquisition proportionally slower, but in places where
+ * it is used (filesystem unmount) performance is not critical.
+ *
+ * All the functions below are direct wrappers around functions above.
+ */
+void
+rrm_init(rrmlock_t *rrl, boolean_t track_all)
+{
+ int i;
+
+ for (i = 0; i < RRM_NUM_LOCKS; i++)
+ rrw_init(&rrl->locks[i], track_all);
+}
+
+void
+rrm_destroy(rrmlock_t *rrl)
+{
+ int i;
+
+ for (i = 0; i < RRM_NUM_LOCKS; i++)
+ rrw_destroy(&rrl->locks[i]);
+}
+
+void
+rrm_enter(rrmlock_t *rrl, krw_t rw, void *tag)
+{
+ if (rw == RW_READER)
+ rrm_enter_read(rrl, tag);
+ else
+ rrm_enter_write(rrl);
+}
+
+/*
+ * This maps the current thread to a specific lock. Note that the lock
+ * must be released by the same thread that acquired it. We do this
+ * mapping by taking the thread pointer mod a prime number. We examine
+ * only the low 32 bits of the thread pointer, because 32-bit division
+ * is faster than 64-bit division, and the high 32 bits have little
+ * entropy anyway.
+ */
+#define RRM_TD_LOCK() (((uint32_t)(uintptr_t)(curthread)) % RRM_NUM_LOCKS)
+
+void
+rrm_enter_read(rrmlock_t *rrl, void *tag)
+{
+ rrw_enter_read(&rrl->locks[RRM_TD_LOCK()], tag);
+}
+
+void
+rrm_enter_write(rrmlock_t *rrl)
+{
+ int i;
+
+ for (i = 0; i < RRM_NUM_LOCKS; i++)
+ rrw_enter_write(&rrl->locks[i]);
+}
+
+void
+rrm_exit(rrmlock_t *rrl, void *tag)
+{
+ int i;
+
+ if (rrl->locks[0].rr_writer == curthread) {
+ for (i = 0; i < RRM_NUM_LOCKS; i++)
+ rrw_exit(&rrl->locks[i], tag);
+ } else {
+ rrw_exit(&rrl->locks[RRM_TD_LOCK()], tag);
+ }
+}
+
+boolean_t
+rrm_held(rrmlock_t *rrl, krw_t rw)
+{
+ if (rw == RW_WRITER) {
+ return (rrw_held(&rrl->locks[0], rw));
+ } else {
+ return (rrw_held(&rrl->locks[RRM_TD_LOCK()], rw));
+ }
+}
if (get_zfs_sb(name, zsbp) != 0)
error = zfs_sb_create(name, zsbp);
if (error == 0) {
- rrw_enter(&(*zsbp)->z_teardown_lock, (writer) ? RW_WRITER :
+ rrm_enter(&(*zsbp)->z_teardown_lock, (writer) ? RW_WRITER :
RW_READER, tag);
if ((*zsbp)->z_unmounted) {
/*
* thread should be just about to disassociate the
* objset from the zsb.
*/
- rrw_exit(&(*zsbp)->z_teardown_lock, tag);
+ rrm_exit(&(*zsbp)->z_teardown_lock, tag);
return (SET_ERROR(EBUSY));
}
}
static void
zfs_sb_rele(zfs_sb_t *zsb, void *tag)
{
- rrw_exit(&zsb->z_teardown_lock, tag);
+ rrm_exit(&zsb->z_teardown_lock, tag);
if (zsb->z_sb) {
deactivate_super(zsb->z_sb);
mutex_init(&zsb->z_lock, NULL, MUTEX_DEFAULT, NULL);
list_create(&zsb->z_all_znodes, sizeof (znode_t),
offsetof(znode_t, z_link_node));
- rrw_init(&zsb->z_teardown_lock, B_FALSE);
+ rrm_init(&zsb->z_teardown_lock, B_FALSE);
rw_init(&zsb->z_teardown_inactive_lock, NULL, RW_DEFAULT, NULL);
rw_init(&zsb->z_fuid_lock, NULL, RW_DEFAULT, NULL);
mutex_destroy(&zsb->z_znodes_lock);
mutex_destroy(&zsb->z_lock);
list_destroy(&zsb->z_all_znodes);
- rrw_destroy(&zsb->z_teardown_lock);
+ rrm_destroy(&zsb->z_teardown_lock);
rw_destroy(&zsb->z_teardown_inactive_lock);
rw_destroy(&zsb->z_fuid_lock);
for (i = 0; i != ZFS_OBJ_MTX_SZ; i++)
}
}
- rrw_enter(&zsb->z_teardown_lock, RW_WRITER, FTAG);
+ rrm_enter(&zsb->z_teardown_lock, RW_WRITER, FTAG);
if (!unmounting) {
/*
*/
if (!unmounting && (zsb->z_unmounted || zsb->z_os == NULL)) {
rw_exit(&zsb->z_teardown_inactive_lock);
- rrw_exit(&zsb->z_teardown_lock, FTAG);
+ rrm_exit(&zsb->z_teardown_lock, FTAG);
return (SET_ERROR(EIO));
}
*/
if (unmounting) {
zsb->z_unmounted = B_TRUE;
- rrw_exit(&zsb->z_teardown_lock, FTAG);
+ rrm_exit(&zsb->z_teardown_lock, FTAG);
rw_exit(&zsb->z_teardown_inactive_lock);
}
znode_t *zp;
uint64_t sa_obj = 0;
- ASSERT(RRW_WRITE_HELD(&zsb->z_teardown_lock));
+ ASSERT(RRM_WRITE_HELD(&zsb->z_teardown_lock));
ASSERT(RW_WRITE_HELD(&zsb->z_teardown_inactive_lock));
/*
bail:
/* release the VFS ops */
rw_exit(&zsb->z_teardown_inactive_lock);
- rrw_exit(&zsb->z_teardown_lock, FTAG);
+ rrm_exit(&zsb->z_teardown_lock, FTAG);
if (err) {
/*
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