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| author | Mingzhe Zou <mingzhe.zou@easystack.cn> | 2022-01-07 16:21:13 +0800 |
|---|---|---|
| committer | Coly Li <colyli@suse.de> | 2022-03-06 22:33:37 +0800 |
| commit | 7b1002f7cfe581930f63787a0b3de0144e61ed55 (patch) | |
| tree | b348bdf5de00503d4ca530cce6880dd15b88832d /drivers/md | |
| parent | 13d4ef0f66b7ee9415e101e213acaf94a0cb28ee (diff) | |
bcache: fixup bcache_dev_sectors_dirty_add() multithreaded CPU false sharing
When attaching a cached device (a.k.a backing device) to a cache
device, bch_sectors_dirty_init() is called to count dirty sectors
and stripes (see what bcache_dev_sectors_dirty_add() does) on the
cache device.
When bcache_dev_sectors_dirty_add() is called, set_bit(stripe,
d->full_dirty_stripes) or clear_bit(stripe, d->full_dirty_stripes)
operation will always be performed. In full_dirty_stripes, each 1bit
represents stripe_size (8192) sectors (512B), so 1bit=4MB (8192*512),
and each CPU cache line=64B=512bit=2048MB. When 20 threads process
a cached disk with 100G dirty data, a single thread processes about
23M at a time, and 20 threads total 460M. These full_dirty_stripes
bits corresponding to the 460M data is likely to fall in the same CPU
cache line. When one of these threads performs a set_bit or clear_bit
operation, the same CPU cache line of other threads will become invalid
and must read the full_dirty_stripes from the main memory again. Compared
with single thread, the time of a bcache_dev_sectors_dirty_add()
call is increased by about 50 times in our test (100G dirty data,
20 threads, bcache_dev_sectors_dirty_add() is called more than
20 million times).
This patch tries to test_bit before set_bit or clear_bit operation.
Therefore, a lot of force set and clear operations will be avoided,
and most of bcache_dev_sectors_dirty_add() calls will only read CPU
cache line.
Signed-off-by: Mingzhe Zou <mingzhe.zou@easystack.cn>
Signed-off-by: Coly Li <colyli@suse.de>
Diffstat (limited to 'drivers/md')
| -rw-r--r-- | drivers/md/bcache/writeback.c | 11 |
1 files changed, 7 insertions, 4 deletions
diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index d42301e6309d..176461f89f46 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -585,10 +585,13 @@ void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned int inode, sectors_dirty = atomic_add_return(s, d->stripe_sectors_dirty + stripe); - if (sectors_dirty == d->stripe_size) - set_bit(stripe, d->full_dirty_stripes); - else - clear_bit(stripe, d->full_dirty_stripes); + if (sectors_dirty == d->stripe_size) { + if (!test_bit(stripe, d->full_dirty_stripes)) + set_bit(stripe, d->full_dirty_stripes); + } else { + if (test_bit(stripe, d->full_dirty_stripes)) + clear_bit(stripe, d->full_dirty_stripes); + } nr_sectors -= s; stripe_offset = 0; |