Bug #37703 MySQL performance with and without Fast Mutexes using Sysbench Workload
Submitted: 27 Jun 2008 21:20 Modified: 29 Apr 2015 0:09
Reporter: Harita Chilukuri Email Updates:
Status: Closed Impact on me:
Category:MySQL Server: General Severity:S5 (Performance)
Version:MYSQL 6.0.4 (Source Distribution) OS:Linux (EL5.1)
Assigned to: CPU Architecture:Any
Tags: fast mutexes
Triage: Triaged: D4 (Minor)

[27 Jun 2008 21:20] Harita Chilukuri
I did some of the work related to MySQL performance with and without fast mutexes. I see that there is no performance difference between them. From the cycles profiling data, it shows that the % cycles is divided among __pthread_mutex_trylock, __pthread_mutex_lock and my_pthread_fastmutex_lock (with fast mutexes) which is equal to the __pthread_mutex_lock ( without fast mutexes. 

I am using IntelĀ® 2x Clovertown (quad core processor) and Sysbench workload.

How to repeat:
Run MYSQL 6.0.4 with and without fast mutexes using sysbench workload.

Suggested fix:
Decrease the number of spins and delays to 2 in MY_PTHREAD_FASTMUTEX_LOCK(). By decreasing the spins and delays, the chances of acquiring a lock increases. This gives ~2.01% gain/improvement in performance.
[21 Aug 2008 4:05] Valeriy Kravchuk
Thank you for a problem report. Please, try to repeat with a newer version, 6.0.6, and inform about the results. In case of the same problem, please, specify the exact sysbench commands used to test.
[18 Sep 2008 16:15] Harita Chilukuri
I cannot try this with 6.0.6 as I do hit this bug http://bugs.mysql.com/bug.php?id=39490, which is fixed in the 6.0.7 version.

Hence, I will post the results using 6.0.7 soon.

[20 Sep 2008 6:59] Valeriy Kravchuk
OK, let's wait for 6.0.7.
[26 Sep 2008 22:52] Harita Chilukuri
I tried the same experiment with MySQL 6.0.7 from the development tree. 

The problem still exists: there is no performance difference at all (within noise range) when mysql is complied with or without fast mutexes. Also, if I reduce the number of spins and delays there is no improvement in the performance (within noise range).

Has there been any specific changes made in this mysql version, as I dont see any performance difference by decreasing the number of spins and delays??

Below is the detailed results:

Test               Transactions per second	CPU utilization(usr sys idle wt)
Without                 90578.66                  73    22    5    0
Fast Mutexes			
With Fast Mutexes	90470.06	          73   22    4    0
Reduced the number 
of spins and delays	 90310.32	           73   22    4    0

Sysbench Tests:

1) ./sysbench prepare --test=oltp --mysql-table-engine=falcon --mysql-engine-trx=yes --mysql-socket=/tmp/mysql.sock  --oltp-table-size=100000 --oltp-test-mode=simple

2) ./sysbench run --num-threads=8 --max-time=220 --max-requests=0 --mysql-table-engine=falcon --mysql-engine-trx=yes --test=oltp --oltp-test-mode=simple --oltp-table-size=100000 --mysql-socket=/tmp/mysql.sock  > $OUTPUT_RESULT_DIR/metrics.out

[17 Oct 2008 3:15] Davi Arnaut
[29 Apr 2015 0:09] Paul Dubois
Noted in 5.7.8 changelog.

The so-called "fast mutex" code has been removed from the server
sources. It provides no measurable benefit, complicates the code, and
is problematic for certain architectures such as POWER8. The
(undocumented) WITH_FAST_MUTEXES CMake option has also been removed.