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bcachefs: Use try_cmpxchg() family of functions instead of cmpxchg()

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Use try_cmpxchg() family of functions instead of
cmpxchg (*ptr, old, new) == old. x86 CMPXCHG instruction returns
success in ZF flag, so this change saves a compare after cmpxchg
(and related move instruction in front of cmpxchg).

Also, try_cmpxchg() implicitly assigns old *ptr value to "old" when
cmpxchg fails. There is no need to re-read the value in the loop.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Brian Foster <bfoster@redhat.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Uros Bizjak 2024-05-23 11:19:26 +02:00 committed by Kent Overstreet
parent e76a2b65b0
commit 68573b936d
11 changed files with 58 additions and 59 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
fs/bcachefs/btree_cache.c
View File

@ -602,8 +602,8 @@ int bch2_btree_cache_cannibalize_lock(struct btree_trans *trans, struct closure
struct btree_cache *bc = &c->btree_cache;
struct task_struct *old;
old = cmpxchg(&bc->alloc_lock, NULL, current);
if (old == NULL || old == current)
old = NULL;
if (try_cmpxchg(&bc->alloc_lock, &old, current) || old == current)
goto success;
if (!cl) {
@ -614,8 +614,8 @@ int bch2_btree_cache_cannibalize_lock(struct btree_trans *trans, struct closure
closure_wait(&bc->alloc_wait, cl);
/* Try again, after adding ourselves to waitlist */
old = cmpxchg(&bc->alloc_lock, NULL, current);
if (old == NULL || old == current) {
old = NULL;
if (try_cmpxchg(&bc->alloc_lock, &old, current) || old == current) {
/* We raced */
closure_wake_up(&bc->alloc_wait);
goto success;

20
fs/bcachefs/btree_io.c
View File

@ -1796,15 +1796,16 @@ int bch2_btree_root_read(struct bch_fs *c, enum btree_id id,
static void bch2_btree_complete_write(struct bch_fs *c, struct btree *b,
struct btree_write *w)
{
unsigned long old, new, v = READ_ONCE(b->will_make_reachable);
unsigned long old, new;
old = READ_ONCE(b->will_make_reachable);
do {
old = new = v;
new = old;
if (!(old & 1))
break;
new &= ~1UL;
} while ((v = cmpxchg(&b->will_make_reachable, old, new)) != old);
} while (!try_cmpxchg(&b->will_make_reachable, &old, new));
if (old & 1)
closure_put(&((struct btree_update *) new)->cl);
@ -1815,14 +1816,14 @@ static void bch2_btree_complete_write(struct bch_fs *c, struct btree *b,
static void __btree_node_write_done(struct bch_fs *c, struct btree *b)
{
struct btree_write *w = btree_prev_write(b);
unsigned long old, new, v;
unsigned long old, new;
unsigned type = 0;
bch2_btree_complete_write(c, b, w);
v = READ_ONCE(b->flags);
old = READ_ONCE(b->flags);
do {
old = new = v;
new = old;
if ((old & (1U << BTREE_NODE_dirty)) &&
(old & (1U << BTREE_NODE_need_write)) &&
@ -1842,7 +1843,7 @@ static void __btree_node_write_done(struct bch_fs *c, struct btree *b)
new &= ~(1U << BTREE_NODE_write_in_flight);
new &= ~(1U << BTREE_NODE_write_in_flight_inner);
}
} while ((v = cmpxchg(&b->flags, old, new)) != old);
} while (!try_cmpxchg(&b->flags, &old, new));
if (new & (1U << BTREE_NODE_write_in_flight))
__bch2_btree_node_write(c, b, BTREE_WRITE_ALREADY_STARTED|type);
@ -2014,8 +2015,9 @@ void __bch2_btree_node_write(struct bch_fs *c, struct btree *b, unsigned flags)
* dirty bit requires a write lock, we can't race with other threads
* redirtying it:
*/
old = READ_ONCE(b->flags);
do {
old = new = READ_ONCE(b->flags);
new = old;
if (!(old & (1 << BTREE_NODE_dirty)))
return;
@ -2046,7 +2048,7 @@ void __bch2_btree_node_write(struct bch_fs *c, struct btree *b, unsigned flags)
new |= (1 << BTREE_NODE_write_in_flight_inner);
new |= (1 << BTREE_NODE_just_written);
new ^= (1 << BTREE_NODE_write_idx);
} while (cmpxchg_acquire(&b->flags, old, new) != old);
} while (!try_cmpxchg_acquire(&b->flags, &old, new));
if (new & (1U << BTREE_NODE_need_write))
return;

8
fs/bcachefs/btree_trans_commit.c
View File

@ -228,14 +228,14 @@ static int __btree_node_flush(struct journal *j, struct journal_entry_pin *pin,
struct btree_write *w = container_of(pin, struct btree_write, journal);
struct btree *b = container_of(w, struct btree, writes[i]);
struct btree_trans *trans = bch2_trans_get(c);
unsigned long old, new, v;
unsigned long old, new;
unsigned idx = w - b->writes;
btree_node_lock_nopath_nofail(trans, &b->c, SIX_LOCK_read);
v = READ_ONCE(b->flags);
old = READ_ONCE(b->flags);
do {
old = new = v;
new = old;
if (!(old & (1 << BTREE_NODE_dirty)) ||
!!(old & (1 << BTREE_NODE_write_idx)) != idx ||
@ -245,7 +245,7 @@ static int __btree_node_flush(struct journal *j, struct journal_entry_pin *pin,
new &= ~BTREE_WRITE_TYPE_MASK;
new |= BTREE_WRITE_journal_reclaim;
new |= 1 << BTREE_NODE_need_write;
} while ((v = cmpxchg(&b->flags, old, new)) != old);
} while (!try_cmpxchg(&b->flags, &old, new));
btree_node_write_if_need(c, b, SIX_LOCK_read);
six_unlock_read(&b->c.lock);

8
fs/bcachefs/btree_update_interior.c
View File

@ -1356,7 +1356,7 @@ static void bch2_insert_fixup_btree_ptr(struct btree_update *as,
struct bch_fs *c = as->c;
struct bkey_packed *k;
struct printbuf buf = PRINTBUF;
unsigned long old, new, v;
unsigned long old, new;
BUG_ON(insert->k.type == KEY_TYPE_btree_ptr_v2 &&
!btree_ptr_sectors_written(insert));
@ -1395,14 +1395,14 @@ static void bch2_insert_fixup_btree_ptr(struct btree_update *as,
bch2_btree_bset_insert_key(trans, path, b, node_iter, insert);
set_btree_node_dirty_acct(c, b);
v = READ_ONCE(b->flags);
old = READ_ONCE(b->flags);
do {
old = new = v;
new = old;
new &= ~BTREE_WRITE_TYPE_MASK;
new |= BTREE_WRITE_interior;
new |= 1 << BTREE_NODE_need_write;
} while ((v = cmpxchg(&b->flags, old, new)) != old);
} while (!try_cmpxchg(&b->flags, &old, new));
printbuf_exit(&buf);
}

17
fs/bcachefs/buckets.c
View File

@ -916,13 +916,13 @@ void bch2_trans_account_disk_usage_change(struct btree_trans *trans)
*/
s64 should_not_have_added = added - (s64) disk_res_sectors;
if (unlikely(should_not_have_added > 0)) {
u64 old, new, v = atomic64_read(&c->sectors_available);
u64 old, new;
old = atomic64_read(&c->sectors_available);
do {
old = v;
new = max_t(s64, 0, old - should_not_have_added);
} while ((v = atomic64_cmpxchg(&c->sectors_available,
old, new)) != old);
} while (!atomic64_try_cmpxchg(&c->sectors_available,
&old, new));
added -= should_not_have_added;
warn = true;
@ -1523,7 +1523,7 @@ int __bch2_disk_reservation_add(struct bch_fs *c, struct disk_reservation *res,
u64 sectors, int flags)
{
struct bch_fs_pcpu *pcpu;
u64 old, v, get;
u64 old, get;
s64 sectors_available;
int ret;
@ -1534,17 +1534,16 @@ int __bch2_disk_reservation_add(struct bch_fs *c, struct disk_reservation *res,
if (sectors <= pcpu->sectors_available)
goto out;
v = atomic64_read(&c->sectors_available);
old = atomic64_read(&c->sectors_available);
do {
old = v;
get = min((u64) sectors + SECTORS_CACHE, old);
if (get < sectors) {
preempt_enable();
goto recalculate;
}
} while ((v = atomic64_cmpxchg(&c->sectors_available,
old, old - get)) != old);
} while (!atomic64_try_cmpxchg(&c->sectors_available,
&old, old - get));
pcpu->sectors_available += get;

4
fs/bcachefs/buckets.h
View File

@ -432,13 +432,13 @@ static inline int bch2_disk_reservation_add(struct bch_fs *c, struct disk_reserv
#ifdef __KERNEL__
u64 old, new;
old = this_cpu_read(c->pcpu->sectors_available);
do {
old = this_cpu_read(c->pcpu->sectors_available);
if (sectors > old)
return __bch2_disk_reservation_add(c, res, sectors, flags);
new = old - sectors;
} while (this_cpu_cmpxchg(c->pcpu->sectors_available, old, new) != old);
} while (!this_cpu_try_cmpxchg(c->pcpu->sectors_available, &old, new));
this_cpu_add(*c->online_reserved, sectors);
res->sectors += sectors;

7
fs/bcachefs/io_write.c
View File

@ -69,11 +69,10 @@ void bch2_latency_acct(struct bch_dev *ca, u64 submit_time, int rw)
u64 io_latency = time_after64(now, submit_time)
? now - submit_time
: 0;
u64 old, new, v = atomic64_read(latency);
u64 old, new;
old = atomic64_read(latency);
do {
old = v;
/*
* If the io latency was reasonably close to the current
* latency, skip doing the update and atomic operation - most of
@ -84,7 +83,7 @@ void bch2_latency_acct(struct bch_dev *ca, u64 submit_time, int rw)
break;
new = ewma_add(old, io_latency, 5);
} while ((v = atomic64_cmpxchg(latency, old, new)) != old);
} while (!atomic64_try_cmpxchg(latency, &old, new));
bch2_congested_acct(ca, io_latency, now, rw);

17
fs/bcachefs/journal.c
View File

@ -230,7 +230,6 @@ static void __journal_entry_close(struct journal *j, unsigned closed_val, bool t
struct bch_fs *c = container_of(j, struct bch_fs, journal);
struct journal_buf *buf = journal_cur_buf(j);
union journal_res_state old, new;
u64 v = atomic64_read(&j->reservations.counter);
unsigned sectors;
BUG_ON(closed_val != JOURNAL_ENTRY_CLOSED_VAL &&
@ -238,15 +237,16 @@ static void __journal_entry_close(struct journal *j, unsigned closed_val, bool t
lockdep_assert_held(&j->lock);
old.v = atomic64_read(&j->reservations.counter);
do {
old.v = new.v = v;
new.v = old.v;
new.cur_entry_offset = closed_val;
if (old.cur_entry_offset == JOURNAL_ENTRY_ERROR_VAL ||
old.cur_entry_offset == new.cur_entry_offset)
return;
} while ((v = atomic64_cmpxchg(&j->reservations.counter,
old.v, new.v)) != old.v);
} while (!atomic64_try_cmpxchg(&j->reservations.counter,
&old.v, new.v));
if (!__journal_entry_is_open(old))
return;
@ -353,7 +353,6 @@ static int journal_entry_open(struct journal *j)
((journal_cur_seq(j) + 1) & JOURNAL_BUF_MASK);
union journal_res_state old, new;
int u64s;
u64 v;
lockdep_assert_held(&j->lock);
BUG_ON(journal_entry_is_open(j));
@ -432,9 +431,9 @@ static int journal_entry_open(struct journal *j)
*/
j->cur_entry_u64s = u64s;
v = atomic64_read(&j->reservations.counter);
old.v = atomic64_read(&j->reservations.counter);
do {
old.v = new.v = v;
new.v = old.v;
BUG_ON(old.cur_entry_offset == JOURNAL_ENTRY_ERROR_VAL);
@ -446,8 +445,8 @@ static int journal_entry_open(struct journal *j)
/* Handle any already added entries */
new.cur_entry_offset = le32_to_cpu(buf->data->u64s);
} while ((v = atomic64_cmpxchg(&j->reservations.counter,
old.v, new.v)) != old.v);
} while (!atomic64_try_cmpxchg(&j->reservations.counter,
&old.v, new.v));
if (nr_unwritten_journal_entries(j) == 1)
mod_delayed_work(j->wq,

8
fs/bcachefs/journal.h
View File

@ -327,10 +327,10 @@ static inline int journal_res_get_fast(struct journal *j,
unsigned flags)
{
union journal_res_state old, new;
u64 v = atomic64_read(&j->reservations.counter);
old.v = atomic64_read(&j->reservations.counter);
do {
old.v = new.v = v;
new.v = old.v;
/*
* Check if there is still room in the current journal
@ -356,8 +356,8 @@ static inline int journal_res_get_fast(struct journal *j,
if (flags & JOURNAL_RES_GET_CHECK)
return 1;
} while ((v = atomic64_cmpxchg(&j->reservations.counter,
old.v, new.v)) != old.v);
} while (!atomic64_try_cmpxchg(&j->reservations.counter,
&old.v, new.v));
res->ref = true;
res->idx = old.idx;

9
fs/bcachefs/journal_io.c
View File

@ -1588,7 +1588,7 @@ static CLOSURE_CALLBACK(journal_write_done)
struct bch_fs *c = container_of(j, struct bch_fs, journal);
struct bch_replicas_padded replicas;
union journal_res_state old, new;
u64 v, seq = le64_to_cpu(w->data->seq);
u64 seq = le64_to_cpu(w->data->seq);
int err = 0;
bch2_time_stats_update(!JSET_NO_FLUSH(w->data)
@ -1647,14 +1647,15 @@ static CLOSURE_CALLBACK(journal_write_done)
if (j->watermark != BCH_WATERMARK_stripe)
journal_reclaim_kick(&c->journal);
v = atomic64_read(&j->reservations.counter);
old.v = atomic64_read(&j->reservations.counter);
do {
old.v = new.v = v;
new.v = old.v;
BUG_ON(journal_state_count(new, new.unwritten_idx));
BUG_ON(new.unwritten_idx != (seq & JOURNAL_BUF_MASK));
new.unwritten_idx++;
} while ((v = atomic64_cmpxchg(&j->reservations.counter, old.v, new.v)) != old.v);
} while (!atomic64_try_cmpxchg(&j->reservations.counter,
&old.v, new.v));
closure_wake_up(&w->wait);
completed = true;

11
fs/bcachefs/two_state_shared_lock.h
View File

@ -36,15 +36,14 @@ static inline void bch2_two_state_unlock(two_state_lock_t *lock, int s)
static inline bool bch2_two_state_trylock(two_state_lock_t *lock, int s)
{
long i = s ? 1 : -1;
long v = atomic_long_read(&lock->v), old;
long old;
old = atomic_long_read(&lock->v);
do {
old = v;
if (i > 0 ? v < 0 : v > 0)
if (i > 0 ? old < 0 : old > 0)
return false;
} while ((v = atomic_long_cmpxchg_acquire(&lock->v,
old, old + i)) != old);
} while (!atomic_long_try_cmpxchg_acquire(&lock->v, &old, old + i));
return true;
}