MySQL Bugs: #97150: rwlock: refine lock->recursive with C11 atomics

Bug #97150	rwlock: refine lock->recursive with C11 atomics
Submitted:	9 Oct 2019 1:37	Modified:	14 Feb 2020 15:52
Reporter:	Cai Yibo (OCA)	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: InnoDB storage engine	Severity:	S5 (Performance)
Version:	8.0	OS:	Any
Assigned to:		CPU Architecture:	ARM
Tags:	Contribution

Description:
This is a followup patch of Bug #96504(Refine atomics and barriers for weak memory order platform), https://bugs.mysql.com/bug.php?id=96504

Setting lock->recursive publishes valid lock->writer_thread, their
ordering must be enforced in both writing and reading side.

Current implementation uses wmb and rmb for this purpose. This patch
leverages C++11 memory model to refine it with store-release and
load-acquire ordering, which is designed for this typical use case
and more friendly to weak memory order platforms like Arm.

Atomic operations of current code are based on GCC __sync_xxx or
__atomic_xxx builtins for Linux and Solaris, and MSVC InterlockedXXX
ones for Windows.[1]

It's hard to add another set of atomic operations with memory order
parameters and keep existing code concise at the same time(without
exploding #ifdef). So I'm using C++11 std::atomic, which is supported
by all compilers per mysql8.0 source installation prerequisites.[2]
Added an os_atomic_t class which wraps std::atomic and does some
refinements, it will also be used in later patches.

[1] https://github.com/mysql/mysql-server/blob/8.0/storage/innobase/include/os0atomic.h
[2] https://dev.mysql.com/doc/refman/8.0/en/source-installation-prerequisites.html

How to repeat:
NA

patch (*) I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

Contribution: 0001-rwlock-refine-lock-recursive-with-C-11-atomics.patch (text/x-patch), 9.23 KiB.

Hi Mr. Yibo,

Thank you for your bug report.

I have analysed your patch and concluded that it is very useful for the ARM platform.

Verified as reported.

Posted by developer:
 
Fixed as of the upcoming 8.0.20 release, and here's the changelog entry:

Read-write lock code (rw_lock_t) that controls ordering of access to the
boolean recursive flag and the writer thread ID using GCC builtins or
os_mutex when the builtins are not available, was revised to use C++
std::atomic in some instances.

Thank you, Daniel.

Posted by developer:
 
Contribution from Cai Yibo is noted in the changelog entry.

The problem exists on the 5.7.31 ARM platform, and we look forward to merging into the 5.7 version

Hi Mr. dong,

It has yet to be decided whether this could be ported to the latest 5.7.

It depends on the existing infrastructure in 5.7 and on the code organisation.