Re: [LKP] [ext4] 05c2c00f37: aim7.jobs-per-min -11.8% regression

[Xing Zhengjun]

Hi Jan,

On 5/20/2021 5:51 PM, Jan Kara wrote:
> Hello!
>
> On Thu 20-05-21 15:13:20, Xing Zhengjun wrote:
> >       Do you have time to look at this? The regression still existed in the
> > latest Linux mainline v5.13-rc2.
>
> Thanks for verification and for the ping! I had a look into this and I
> think the regression is caused by the changes in orphan handling. The load
> runs multiple tasks all creating and deleting files. This generally
> contends on the orphan locking with fast storage (which is your case
> because you use ramdisk as a backing store AFAICT). And the changes I did
> move superblock checksum computation under the orphan lock so the lock hold
> times are now higher.
>
> Sadly it is not easy to move checksum update from under the orphan lock and
> maintain checksum consistency since the checksum has to be recomputed
> consistently with the changes of superblock state. But I have one idea how
> we could maybe improve the situation. Can you check whether attached patch
> recovers the regression? Because that's about how good it could get when we
> are more careful when writing out superblock.
>
> 								Honza

I apply the patch based on v5.13-rc2 and test, it can not recover the 
regression and the regression became more serious(-45.7%).

=========================================================================================
tbox_group/testcase/rootfs/kconfig/compiler/disk/md/fs/test/load/cpufreq_governor/ucode:

lkp-csl-2sp9/aim7/debian-10.4-x86_64-20200603.cgz/x86_64-rhel-8.3/gcc-9/4BRD_12G/RAID1/ext4/creat-clo/1000/performance/0x5003006

commit:
  4392fbc4bab57db3760f0fb61258cb7089b37665
  05c2c00f3769abb9e323fcaca70d2de0b48af7ba
  v5.13-rc2
  2a1eb1a2fc08daaaf76a5aa8ffa355b5a5013d86    (the test patch)

4392fbc4bab57db3 05c2c00f3769abb9e323fcaca70                   v5.13-rc2 
2a1eb1a2fc08daaaf76a5aa8ffa
---------------- --------------------------- --------------------------- 
---------------------------
         %stddev     %change         %stddev     %change 
%stddev     %change         %stddev
             \          |                \          |                \ 
         |                \
     13342           -11.8%      11771 ±  2%     -14.2%      11450 
      -45.7%       7240 ±  3%  aim7.jobs-per-min



--
Zhengjun Xing