[PATCH v2 0/3] debugobjects: Reduce global pool_lock contention

From: Waiman Long
Date: Fri Dec 02 2016 - 16:16:03 EST


v1->v2:
- Move patch 2 in front of patch 1.
- Fix merge conflict with linux-next.

This patchset aims to reduce contention of the global pool_lock
while improving performance at the same time. It is done to resolve
the following soft lockup problem with a debug kernel in some of the
large SMP systems:

NMI watchdog: BUG: soft lockup - CPU#35 stuck for 22s! [rcuos/1:21]
...
RIP: 0010:[<ffffffff817c216b>] [<ffffffff817c216b>]
_raw_spin_unlock_irqrestore+0x3b/0x60
...
Call Trace:
[<ffffffff813f40d1>] free_object+0x81/0xb0
[<ffffffff813f4f33>] debug_check_no_obj_freed+0x193/0x220
[<ffffffff81101a59>] ? trace_hardirqs_on_caller+0xf9/0x1c0
[<ffffffff81284996>] ? file_free_rcu+0x36/0x60
[<ffffffff81251712>] kmem_cache_free+0xd2/0x380
[<ffffffff81284960>] ? fput+0x90/0x90
[<ffffffff81284996>] file_free_rcu+0x36/0x60
[<ffffffff81124c23>] rcu_nocb_kthread+0x1b3/0x550
[<ffffffff81124b71>] ? rcu_nocb_kthread+0x101/0x550
[<ffffffff81124a70>] ? sync_exp_work_done.constprop.63+0x50/0x50
[<ffffffff810c59d1>] kthread+0x101/0x120
[<ffffffff81101a59>] ? trace_hardirqs_on_caller+0xf9/0x1c0
[<ffffffff817c2d32>] ret_from_fork+0x22/0x50

On a 8-socket IvyBridge-EX system (120 cores, 240 threads), the
elapsed time of a 4.9-rc7 kernel parallel build (make -j 240) was
reduced from 7m57s to 7m19s with a patched 4.9-rc7 kernel. There
was also about a 10X reduction in the number of debug objects being
allocated from or freed to the kmemcache during the kernel build.

Waiman Long (3):
debugobjects: Track number of kmem_cache_alloc/kmem_cache_free done
debugobjects: Scale thresholds with # of CPUs
debugobjects: Reduce contention on the global pool_lock

lib/debugobjects.c | 57 ++++++++++++++++++++++++++++++++++++++++++------------
1 file changed, 45 insertions(+), 12 deletions(-)

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1.8.3.1