[PATCH v2 0/2] Make reader optimistic spinning optional

[Bongkyu Kim]

Hi,

This is rework of the following discussed patch.
https://lore.kernel.org/all/20230613043308.GA1027@xxxxxxxxxxxxxxxxxxxxxxxxx/

Changes from the previous patch
- Split to revert and modify patches
- Change according to Waiman Long's review
    More wording to documentation part
    Change module_param to early_param
    Code change by Waiman Long's suggestion

In mobile environment, reader optimistic spinning is still useful
because there're not many readers. In my test result at android device,
it improves application startup time about 3.8%
App startup time is most important factor for android user expriences.
So, re-enable reader optimistic spinning by this commit. And,
make it optional feature by cmdline.

Test result:
This is 15 application startup performance in our exynos soc.
- Cortex A78*2 + Cortex A55*6
- unit: ms (lower is better)

Application             base  opt_rspin  Diff  Diff(%)
--------------------  ------  ---------  ----  -------
* Total(geomean)         343        330   -13    +3.8%
--------------------  ------  ---------  ----  -------
helloworld               110        108    -2    +1.8%
Amazon_Seller            397        388    -9    +2.3%
Whatsapp                 311        304    -7    +2.3%
Simple_PDF_Reader        500        463   -37    +7.4%
FaceApp                  330        317   -13    +3.9%
Timestamp_Camera_Free    451        443    -8    +1.8%
Kindle                   629        597   -32    +5.1%
Coinbase                 243        233   -10    +4.1%
Firefox                  425        399   -26    +6.1%
Candy_Crush_Soda         552        538   -14    +2.5%
Hill_Climb_Racing        245        230   -15    +6.1%
Call_Recorder            437        426   -11    +2.5%
Color_Fill_3D            190        180   -10    +5.3%
eToro                    512        505    -7    +1.4%
GroupMe                  281        266   -15    +5.3%

Changes v1 -> v2:
- Move the rwsem_opt_rspin definition out of the "ifdef
  CONFIG_RWSEM_SPIN_ON_OWNER" and add _ro_after_init to rwsem_opt_rspin.

Bongkyu Kim (2):
  Revert "locking/rwsem: Remove reader optimistic spinning"
  locking/rwsem: Make reader optimistic spinning optional

 .../admin-guide/kernel-parameters.txt         |   9 +
 kernel/locking/lock_events_list.h             |   5 +-
 kernel/locking/rwsem.c                        | 297 +++++++++++++++---
 3 files changed, 263 insertions(+), 48 deletions(-)

-- 
2.36.1