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Subject[PATCH v2 0/5] locking/lockdep: Improve lockdep performance
- Minor twists to incorporate Ingo's comments.
- Move class->ops from the lock_class structure to percpu array under
CONFIG_DEBUG_LOCKDEP. That moves the increased memory consumption

Enabling CONFIG_LOCKDEP and other related debug options will greatly
reduce system performance. This patchset aims to reduce the performance
slowdown caused by the lockdep code.

Patch 1 just removes an inline function that wasn't used.

Patches 2 and 3 are minor twists to optimize the code.

Patch 4 makes class->ops a per-cpu counter and moves the stat counter

Patch 5 moves the lock_release() call outside of the lock critical

Parallel kernel compilation tests (make -j <#cpu>, best of 3 runs)
with gcc8 were performed on 2 different systems:

1) an 1-socket 22-core 44-thread Skylake system
2) a 4-socket 72-core 144-thread Broadwell system

Four different kernel variants based on the 4.19-rc5 kernel were used:

1) non-debug kernel (with minimal debug options enabled)
2) pre-patch debug kernel (CONFIG_LOCKDEP, !CONFIG_DEBUG_LOCKDEP)
3) post-patch debug kernel (CONFIG_LOCKDEP, !CONFIG_DEBUG_LOCKDEP)
4) post-patch debug kernel (CONFIG_LOCKDEP, CONFIG_DEBUG_LOCKDEP)

Note that the debug kernels had more debug options enabled than just

The build times with pre-patch and post-patch debug kernels were:

System Kernel 1 Kernel 2 Kernel 3 Kernel 4
------ -------- -------- -------- --------
1-socket 6m06.0s 8m54.7s 8m34.9s 9m28.1s
4-socket 4m09.2s 7m36.0s 5m38.8s 6m17.8s

Using the non-debug kernel execution times as the baseline, the %
runtime increase of the other 3 kernel variants were:

System Kernel 2 Kernel 3 Kernel 4
------ -------- -------- --------
1-socket +46.1% +40.7% +55.2%
4-socket +83.0% +36.0% +51.6%

Comparing just kernels 2 and 3, the patch reduced the execution times
by 3.7% and 25.7% for the 1-socket and 4-socket systems respectively.

I think the last 2 patches yield most of the performance improvement.

Waiman Long (5):
locking/lockdep: Remove add_chain_cache_classes()
locking/lockdep: Eliminate redundant irqs check in __lock_acquire()
locking/lockdep: Add a faster path in __lock_release()
locking/lockdep: Make class->ops a percpu counter
locking/lockdep: Call lock_release() after releasing the lock

include/linux/lockdep.h | 7 +-
include/linux/rwlock_api_smp.h | 16 ++--
include/linux/spinlock_api_smp.h | 8 +-
kernel/locking/lockdep.c | 113 ++++++++---------------------
kernel/locking/lockdep_internals.h | 23 ++++++
kernel/locking/lockdep_proc.c | 2 +-
6 files changed, 66 insertions(+), 103 deletions(-)


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