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authorWaiman Long <longman@redhat.com>2018-10-16 09:45:06 -0400
committerIngo Molnar <mingo@kernel.org>2018-10-17 08:37:31 +0200
commit1222109a53637f96c581224198b86856d503f892 (patch)
treee144300a8e2e0d4121f02571097e43d49e45bf4a /kernel/locking
parent7aa54be2976550f17c11a1c3e3630002dea39303 (diff)
downloadlinux-1222109a53637f96c581224198b86856d503f892.tar.bz2
locking/qspinlock_stat: Count instances of nested lock slowpaths
Queued spinlock supports up to 4 levels of lock slowpath nesting - user context, soft IRQ, hard IRQ and NMI. However, we are not sure how often the nesting happens. So add 3 more per-CPU stat counters to track the number of instances where nesting index goes to 1, 2 and 3 respectively. On a dual-socket 64-core 128-thread Zen server, the following were the new stat counter values under different circumstances: State slowpath index1 index2 index3 ----- -------- ------ ------ ------- After bootup 1,012,150 82 0 0 After parallel build + perf-top 125,195,009 82 0 0 So the chance of having more than 2 levels of nesting is extremely low. [ mingo: Minor changelog edits. ] Signed-off-by: Waiman Long <longman@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Link: http://lkml.kernel.org/r/1539697507-28084-1-git-send-email-longman@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/qspinlock.c5
-rw-r--r--kernel/locking/qspinlock_stat.h6
2 files changed, 11 insertions, 0 deletions
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 341ca666bc60..ce6af1ee2cac 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -397,6 +397,11 @@ pv_queue:
node += idx;
/*
+ * Keep counts of non-zero index values:
+ */
+ qstat_inc(qstat_lock_idx1 + idx - 1, idx);
+
+ /*
* Ensure that we increment the head node->count before initialising
* the actual node. If the compiler is kind enough to reorder these
* stores, then an IRQ could overwrite our assignments.
diff --git a/kernel/locking/qspinlock_stat.h b/kernel/locking/qspinlock_stat.h
index 6bd78c0740fc..42d3d8dc8f49 100644
--- a/kernel/locking/qspinlock_stat.h
+++ b/kernel/locking/qspinlock_stat.h
@@ -55,6 +55,9 @@ enum qlock_stats {
qstat_pv_wait_node,
qstat_lock_pending,
qstat_lock_slowpath,
+ qstat_lock_idx1,
+ qstat_lock_idx2,
+ qstat_lock_idx3,
qstat_num, /* Total number of statistical counters */
qstat_reset_cnts = qstat_num,
};
@@ -82,6 +85,9 @@ static const char * const qstat_names[qstat_num + 1] = {
[qstat_pv_wait_node] = "pv_wait_node",
[qstat_lock_pending] = "lock_pending",
[qstat_lock_slowpath] = "lock_slowpath",
+ [qstat_lock_idx1] = "lock_index1",
+ [qstat_lock_idx2] = "lock_index2",
+ [qstat_lock_idx3] = "lock_index3",
[qstat_reset_cnts] = "reset_counters",
};