Re: [PATCH v2] buffer: Avoid setting buffer bits that are already set

[kemi <kemi.wang@intel.com>]

Hi, Jens
  Could you help to merge this patch to your tree? Thanks

On 2017年11月03日 10:29, kemi wrote:
> 
> 
> On 2017年10月24日 09:16, Kemi Wang wrote:
>> It's expensive to set buffer flags that are already set, because that
>> causes a costly cache line transition.
>>
>> A common case is setting the "verified" flag during ext4 writes.
>> This patch checks for the flag being set first.
>>
>> With the AIM7/creat-clo benchmark testing on a 48G ramdisk based-on ext4
>> file system, we see 3.3%(15431->15936) improvement of aim7.jobs-per-min on
>> a 2-sockets broadwell platform.
>>
>> What the benchmark does is: it forks 3000 processes, and each  process do
>> the following:
>> a) open a new file
>> b) close the file
>> c) delete the file
>> until loop=100*1000 times.
>>
>> The original patch is contributed by Andi Kleen.
>>
>> Signed-off-by: Andi Kleen <ak@linux.intel.com>
>> Signed-off-by: Kemi Wang <kemi.wang@intel.com>
>> Tested-by: Kemi Wang <kemi.wang@intel.com>
>> Reviewed-by: Jens Axboe <axboe@kernel.dk>
>> ---
> 
> Seems that this patch is still not merged. Anything wrong with that? thanks
> 
>>  include/linux/buffer_head.h | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
>> index c8dae55..211d8f5 100644
>> --- a/include/linux/buffer_head.h
>> +++ b/include/linux/buffer_head.h
>> @@ -80,11 +80,14 @@ struct buffer_head {
>>  /*
>>   * macro tricks to expand the set_buffer_foo(), clear_buffer_foo()
>>   * and buffer_foo() functions.
>> + * To avoid reset buffer flags that are already set, because that causes
>> + * a costly cache line transition, check the flag first.
>>   */
>>  #define BUFFER_FNS(bit, name)						\
>>  static __always_inline void set_buffer_##name(struct buffer_head *bh)	\
>>  {									\
>> -	set_bit(BH_##bit, &(bh)->b_state);				\
>> +	if (!test_bit(BH_##bit, &(bh)->b_state))			\
>> +		set_bit(BH_##bit, &(bh)->b_state);              \
>>  }									\
>>  static __always_inline void clear_buffer_##name(struct buffer_head *bh)	\
>>  {									\
>>