Bug #52806 Make InnoDB mutexes green

• Submitted: 14 Apr 2010 6:32
• Modified: 26 Jan 2022 12:34
• Reporter: Mark Callaghan
• Status: Closed
• Category: MySQL Server: InnoDB Plugin storage engine
• Severity: S5 (Performance)
• Version: 5.1
• OS: Any
• Assigned to: Assigned Account
• CPU Architecture: Any
• Tags: green, innodb, mutex

[14 Apr 2010 6:32] Mark Callaghan

Description:
The InnoDB mutex wakes all waiting threads on unlock. This wastes CPU power as only 1 threads can get the lock. NPTL mutex code wakes one thread using futex calls -- read the glibc source. I know InnoDB can do something similar. I even hacked up a change to do this and produced sysbench numbers that match performance without the change while cutting CPU consumption in half.

How to repeat:
Run a test with a lot of mutex contention

Suggested fix:
Wake one thread instead of all threads.

[16 Oct 2012 15:16] Mark Callaghan

More details at https://www.facebook.com/notes/mysql-at-facebook/green-mutexes/10151060544265933

[17 Oct 2012 18:05] Mark Callaghan

More details at https://www.facebook.com/notes/mysql-at-facebook/green-mutexes-part-2/10151061901390933

[26 Jan 2022 12:34] MySQL Verification Team

This was fixed in WL#6044 and pushed to 5.7.2. By using futexes on Linux we
can replace the condition variable broadcast with a "signal".

This bug should be closed.