Re: [PATCH 0/6] Switch arm64 over to qrwlock

From: Jeremy Linton
Date: Thu Oct 05 2017 - 18:13:00 EST


On 10/05/2017 07:54 AM, Will Deacon wrote:
Hi all,

This patch series reworks bits of the qrwlock code that it can be used
to replace the asm rwlocks currently implemented for arm64. The structure
of the series is:

Patches 1-3 : Work WFE into qrwlock using atomic_cond_read_acquire so
we can avoid busy-waiting.

Patch 4 : Enable qrwlocks for arm64

Patch 5-6 : Ensure writer slowpath fairness. This has a potential
performance impact on the writer unlock path, so I've
kept them at the end.

The patches apply on top of my other locking cleanups:

although the conflict with mainline is trivial to resolve without those.
The full stack is also pushed here:

git:// qrwlock

All comments (particularly related to testing and performance) welcome!

I haven't done any perf testing, but the machines continue to boot, and the stress-ng test which causes task lock problems with the normal arm64 rwlock now appears to run as expected. So, its a good start!




Will Deacon (6):
kernel/locking: Use struct qrwlock instead of struct __qrwlock
locking/atomic: Add atomic_cond_read_acquire
kernel/locking: Use atomic_cond_read_acquire when spinning in qrwlock
arm64: locking: Move rwlock implementation over to qrwlocks
kernel/locking: Prevent slowpath writers getting held up by fastpath
kernel/locking: Remove unused union members from struct qrwlock

arch/arm64/Kconfig | 17 ++++
arch/arm64/include/asm/Kbuild | 1 +
arch/arm64/include/asm/spinlock.h | 164 +-------------------------------
arch/arm64/include/asm/spinlock_types.h | 6 +-
include/asm-generic/atomic-long.h | 3 +
include/asm-generic/qrwlock.h | 14 +--
include/asm-generic/qrwlock_types.h | 2 +-
include/linux/atomic.h | 4 +
kernel/locking/qrwlock.c | 83 +++-------------
9 files changed, 43 insertions(+), 251 deletions(-)