Re: [PATCH] bcache: optimize barrier usage for Rmw atomic bitops
From: Coly Li <hidden>
Date: 2020-03-20 15:24:54
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On 2020/1/30 2:08 上午, Davidlohr Bueso wrote:
We can avoid the unnecessary barrier on non LL/SC architectures, such as x86. Instead, use the smp_mb__after_atomic().
Hi Davidlohr,
Signed-off-by: Davidlohr Bueso <redacted>
Sorry for replying late. Indeed we don't need to worry about the extra smp_mb() because the code patch gets called every 5 seconds by default, which is very infrequent. But I like this more accurate patch, it is in my testing already. And by your inspiration, I also fix some other locations to use smp_mb__before/after_atomic(). Thank you. Coly Li
quoted hunk ↗ jump to hunk
--- drivers/md/bcache/writeback.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 4a40f9eadeaf..284ff10f480f 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c@@ -183,7 +183,7 @@ static void update_writeback_rate(struct work_struct *work) */ set_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags); /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */ - smp_mb(); + smp_mb__after_atomic(); /* * CACHE_SET_IO_DISABLE might be set via sysfs interface,@@ -193,7 +193,7 @@ static void update_writeback_rate(struct work_struct *work) test_bit(CACHE_SET_IO_DISABLE, &c->flags)) { clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags); /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */ - smp_mb(); + smp_mb__after_atomic(); return; }@@ -229,7 +229,7 @@ static void update_writeback_rate(struct work_struct *work) */ clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags); /* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */ - smp_mb(); + smp_mb__after_atomic(); } static unsigned int writeback_delay(struct cached_dev *dc,
-- Coly Li