android/android_kernel_asus_sm8350
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

locking/qspinlock_stat: Count instances of nested lock slowpaths

Browse Source 
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>
This commit is contained in:
Waiman Long 2018-10-16 09:45:06 -04:00 committed by Ingo Molnar
parent 7aa54be297
commit 1222109a53
2 changed files with 11 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
kernel/locking/qspinlock.c
View File

@ -396,6 +396,11 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
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

6
kernel/locking/qspinlock_stat.h
View File

@ -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",
};