From eb9b6666d6ca6f3d9f218fa23ec6135eee1ac3a7 Mon Sep 17 00:00:00 2001 From: Coly Li Date: Sun, 22 Mar 2020 14:03:05 +0800 Subject: [PATCH] bcache: optimize barrier usage for atomic operations The idea of this patch is from Davidlohr Bueso, he posts a patch for bcache to optimize barrier usage for read-modify-write atomic bitops. Indeed such optimization can also apply on other locations where smp_mb() is used before or after an atomic operation. This patch replaces smp_mb() with smp_mb__before_atomic() or smp_mb__after_atomic() in btree.c and writeback.c, where it is used to synchronize memory cache just earlier on other cores. Although the locations are not on hot code path, it is always not bad to mkae things a little better. Signed-off-by: Coly Li Cc: Davidlohr Bueso Signed-off-by: Jens Axboe --- drivers/md/bcache/btree.c | 6 +++--- drivers/md/bcache/writeback.c | 6 +++--- 2 files changed, 6 insertions(+), 6 deletions(-) diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c index 74d66b6..72856e5 100644 --- a/drivers/md/bcache/btree.c +++ b/drivers/md/bcache/btree.c @@ -1947,7 +1947,7 @@ static int bch_btree_check_thread(void *arg) */ atomic_set(&check_state->enough, 1); /* Update check_state->enough earlier */ - smp_mb(); + smp_mb__after_atomic(); goto out; } skip_nr--; @@ -1972,7 +1972,7 @@ static int bch_btree_check_thread(void *arg) out: info->result = ret; /* update check_state->started among all CPUs */ - smp_mb(); + smp_mb__before_atomic(); if (atomic_dec_and_test(&check_state->started)) wake_up(&check_state->wait); @@ -2031,7 +2031,7 @@ int bch_btree_check(struct cache_set *c) */ for (i = 0; i < check_state->total_threads; i++) { /* fetch latest check_state->enough earlier */ - smp_mb(); + smp_mb__before_atomic(); if (atomic_read(&check_state->enough)) break; diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 72ba6d0..3f7641f 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -854,7 +854,7 @@ static int bch_dirty_init_thread(void *arg) else { atomic_set(&state->enough, 1); /* Update state->enough earlier */ - smp_mb(); + smp_mb__after_atomic(); goto out; } skip_nr--; @@ -873,7 +873,7 @@ static int bch_dirty_init_thread(void *arg) out: /* In order to wake up state->wait in time */ - smp_mb(); + smp_mb__before_atomic(); if (atomic_dec_and_test(&state->started)) wake_up(&state->wait); @@ -932,7 +932,7 @@ void bch_sectors_dirty_init(struct bcache_device *d) for (i = 0; i < state->total_threads; i++) { /* Fetch latest state->enough earlier */ - smp_mb(); + smp_mb__before_atomic(); if (atomic_read(&state->enough)) break; -- 2.7.4