On 2020/3/23 3:08 下午, Hannes Reinecke wrote:
> On 3/22/20 7:03 AM, Coly Li wrote:
>> From: Davidlohr Bueso <dave@xxxxxxxxxxxx>
>>
>> We can avoid the unnecessary barrier on non LL/SC architectures,
>> such as x86. Instead, use the smp_mb__after_atomic().
>>
>> Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
>> Signed-off-by: Coly Li <colyli@xxxxxxx>
>> ---
>> 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 6673a37c8bd2..72ba6d015786 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,
>>
> Personally, I'd typically tend to use 'test_and_set_bit', as this not
> only implies a barrier, but also captures any errors; if you just use
> 'set_bit' you'll never know if the bit had been set already.
Copied. There are other locations may optimize with test_and_set_bit(),
for example the cannibalize_lock stuffs. I will post all the
test_and_set_bit()/test_and_clear_bit() optimization as another series
later.
Thanks.
--
Coly Li
