[MDEV-26855] Enable spinning for log_sys_mutex and log_flush_order_mutex Created: 2021-10-19  Updated: 2023-03-08  Resolved: 2021-10-19

Status: Closed
Project: MariaDB Server
Component/s: Storage Engine - InnoDB
Affects Version/s: 10.6
Fix Version/s: 10.6.5

Type: Bug Priority: Major
Reporter: Krunal Bauskar Assignee: Marko Mäkelä
Resolution: Fixed Votes: 0
Labels: performance

Attachments: PNG File arm.png     PNG File x86.png    
Issue Links:
Duplicate
is duplicated by MDEV-30481 Hard lock up with queries in "Opening... Closed
Relates
relates to MDEV-23855 InnoDB log checkpointing causes regre... Closed

 Description   

As part of MDEV-26779 we first discovered the effect of enabling spinning for some critical mutex.
MDEV-26779 tried enabling it for lock_sys.wait_mutex and observed a good gain in performance.

In yet another discussion, Mark Callaghan pointed to a reference to pthread based mutex spin using PTHREAD_MUTEX_ADAPTIVE_NP (MDEV-26769 Intel RTM).

Given the strong references, Marko Makela as part of his comment in #1923 pointed an idea to enable
spinning for other mutexes. Based on perf profiling we decided to explore spinning for
log_sys_mutex and log_flush_order_mutex as they are occupying the top slots in the contented mutex list.

The evaluation showed promising results for ARM64 but not for x86.
So a patch is here-by proposed to enable the spinning of the mutex for ARM-based platform.

 Comments   
Comment by Krunal Bauskar [ 2021-10-19 ]

patch submitted: https://github.com/MariaDB/server/pull/1935

Comment by Krunal Bauskar [ 2021-10-19 ]

On ARM, performance gain in the range of 10-60% is observed.

Comment by Marko Mäkelä [ 2021-10-19 ]

The spinloops were deliberately disabled as part of MDEV-23855 already in MariaDB Server 10.5.7.

Several things have changed between 10.5 and 10.6, so it is not too surprising that the spinning may be helpful again.

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