Re: [LKP] [fs/locks] 83b381078b: will-it-scale.per_thread_ops -62.5% regression

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Tue, Nov 27 2018, J. Bruce Fields wrote:

> Thanks for the report!

Yes, thanks.  I thought I had replied to the previous report of a similar
problem, but I didn't actually send that email - oops.
Though the test is the same and the regression similar, this is a
different patch.  The previous report identified 
 fs/locks: allow a lock request to block other requests
this one identifies
  fs/locks: always delete_block after waiting.

Both cause blocked_lock_lock to be taken more often.

In one case is it due to locks_move_blocks().  That can probably be
optimised to skip the lock if list_empty(&fl->fl_blocked_requests).
I'd need to double-check, but I think that is safe to check without
locking.

This one causes locks_delete_blocks() to be called more often.  We now
call it even if no waiting happened at all.  I suspect we can test for
that and avoid it.  I'll have a look.

>
> On Tue, Nov 27, 2018 at 02:01:02PM +0800, kernel test robot wrote:
>> FYI, we noticed a -62.5% regression of will-it-scale.per_thread_ops due to commit:
>> 
>> 
>> commit: 83b381078b5ecab098ebf6bc9548bb32af1dbf31 ("fs/locks: always delete_block after waiting.")
>> https://git.kernel.org/cgit/linux/kernel/git/jlayton/linux.git locks-next
>> 
>> in testcase: will-it-scale
>> on test machine: 88 threads Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz with 64G memory
>> with following parameters:
>> 
>> 	nr_task: 16
>> 	mode: thread
>> 	test: lock1
>
> So I guess it's doing this, uncontended file lock/unlock?:
>
> 	https://github.com/antonblanchard/will-it-scale/blob/master/tests/lock1.c
>
> Each thread is repeatedly locking and unlocking a file that is only used
> by that thread.

Thanks for identifying that Bruce.
This would certainly be a case where locks_delete_block() is now being
called when it wasn't before.


>
> By the way, what's the X-axis on these graphs?  (Or the y-axis, for that
> matter?)

A key would help.  I think the X-axis is number-of-threads.  y-axis
might be ops-per-second ??.

Thanks,
NeilBrown


>
> --b.
>
>>                             will-it-scale.per_thread_ops                        
>>                                                                                 
>>   450000 +-+----------------------------------------------------------------+   
>>          |                                                                  |   
>>   400000 +-+   +..+..  .+..+..  .+..+..+...+..+..+..   +..        .+..    ..|   
>>   350000 +-+ ..      +.       +.                     ..         +.    +..+  |   
>>          |  +                                       +     +     :           |   
>>   300000 +-+                                              :    :            |   
>>   250000 +-+                                               :   :            |   
>>          |                                                 :   :            |   
>>   200000 +-+                                               :   :            |   
>>   150000 +-+                                                : :             |   
>>          O  O  O  O  O  O  O  O  O  O  O   O  O  O  O  O  O :O: O  O  O  O  O   
>>   100000 +-+                                                : :             |   
>>    50000 +-+                                                : :             |   
>>          |                                                   :              |   
>>        0 +-+----------------------------------------------------------------+   
>>                                                                                 
>>                                                                                                                                                                 
>>                                will-it-scale.workload                           
>>                                                                                 
>>   7e+06 +-+-----------------------------------------------------------------+   
>>         |              +...+..           .+..+..+     +            +..      |   
>>   6e+06 +-+   +..+.. ..         .+..+..+.        +   + +         ..       ..|   
>>         |   ..      +         +.                  + +   +       +     +..+  |   
>>   5e+06 +-++                                       +     +      :           |   
>>         |                                                :     :            |   
>>   4e+06 +-+                                               :    :            |   
>>         |                                                 :    :            |   
>>   3e+06 +-+                                                :   :            |   
>>         |                                       O     O    :  : O  O        |   
>>   2e+06 O-+O  O  O  O  O   O  O  O  O  O  O  O     O     O : O:       O  O  O   
>>         |                                                   : :             |   
>>   1e+06 +-+                                                 : :             |   
>>         |                                                    :              |   
>>       0 +-+-----------------------------------------------------------------+   
>>                                                                                 
>>                                                                                                                                                                 
>>                            will-it-scale.time.user_time                         
>>                                                                                 
>>   250 +-+-------------------------------------------------------------------+   
>>       |                 .+..               .+..                   +..       |   
>>       |..   +...+..  .+.      .+...+..+..+.    +..    +..       ..   .    ..|   
>>   200 +-+ ..       +.       +.                    . ..         +      +..+  |   
>>       |  +                                         +     +     :            |   
>>       |                                                  :    :             |   
>>   150 +-+                                                 :   :             |   
>>       |                                                   :   :             |   
>>   100 +-+                                                 :   :             |   
>>       |  O      O                                          : :              |   
>>       O     O      O  O  O  O  O   O  O  O  O  O   O  O  O :O: O  O   O  O  O   
>>    50 +-+                                                  : :              |   
>>       |                                                    : :              |   
>>       |                                                     :               |   
>>     0 +-+-------------------------------------------------------------------+   
>>                                                                                 
>>                                                                                                                                                                 
>>                           will-it-scale.time.system_time                        
>>                                                                                 
>>   5000 +-+------------------------------------------------------------------+   
>>   4500 O-+O..O..O...O..O..O..O..O..O..O...O..O..O..O..O..O  O  O...O..O..O..O   
>>        |                                                 :     :            |   
>>   4000 +-+                                               :     :            |   
>>   3500 +-+                                                :   :             |   
>>        |                                                  :   :             |   
>>   3000 +-+                                                :   :             |   
>>   2500 +-+                                                :   :             |   
>>   2000 +-+                                                 : :              |   
>>        |                                                   : :              |   
>>   1500 +-+                                                 : :              |   
>>   1000 +-+                                                 : :              |   
>>        |                                                    :               |   
>>    500 +-+                                                  :               |   
>>      0 +-+------------------------------------------------------------------+   
>>                                                                                 
>>                                                                                 
>> [*] bisect-good sample
>> [O] bisect-bad  sample

Attachment: signature.asc
Description: PGP signature


[Index of Archives]     [Linux Filesystem Development]     [Linux USB Development]     [Linux Media Development]     [Video for Linux]     [Linux NILFS]     [Linux Audio Users]     [Yosemite Info]     [Linux SCSI]

  Powered by Linux