linux/kernel/locking/qspinlock_stat.h
Waiman Long fb346fd9fc locking/lock_events: Make lock_events available for all archs & other locks
The QUEUED_LOCK_STAT option to report queued spinlocks event counts
was previously allowed only on x86 architecture. To make the locking
event counting code more useful, it is now renamed to a more generic
LOCK_EVENT_COUNTS config option. This new option will be available to
all the architectures that use qspinlock at the moment.

Other locking code can now start to use the generic locking event
counting code by including lock_events.h and put the new locking event
names into the lock_events_list.h header file.

My experience with lock event counting is that it gives valuable insight
on how the locking code works and what can be done to make it better. I
would like to extend this benefit to other locking code like mutex and
rwsem in the near future.

The PV qspinlock specific code will stay in qspinlock_stat.h. The
locking event counters will now reside in the <debugfs>/lock_event_counts
directory.

Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
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: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Link: http://lkml.kernel.org/r/20190404174320.22416-9-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2019-04-10 10:56:04 +02:00

151 lines
3.4 KiB
C

/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* Authors: Waiman Long <longman@redhat.com>
*/
#include "lock_events.h"
#ifdef CONFIG_LOCK_EVENT_COUNTS
#ifdef CONFIG_PARAVIRT_SPINLOCKS
/*
* Collect pvqspinlock locking event counts
*/
#include <linux/sched.h>
#include <linux/sched/clock.h>
#include <linux/fs.h>
#define EVENT_COUNT(ev) lockevents[LOCKEVENT_ ## ev]
/*
* PV specific per-cpu counter
*/
static DEFINE_PER_CPU(u64, pv_kick_time);
/*
* Function to read and return the PV qspinlock counts.
*
* The following counters are handled specially:
* 1. pv_latency_kick
* Average kick latency (ns) = pv_latency_kick/pv_kick_unlock
* 2. pv_latency_wake
* Average wake latency (ns) = pv_latency_wake/pv_kick_wake
* 3. pv_hash_hops
* Average hops/hash = pv_hash_hops/pv_kick_unlock
*/
ssize_t lockevent_read(struct file *file, char __user *user_buf,
size_t count, loff_t *ppos)
{
char buf[64];
int cpu, id, len;
u64 sum = 0, kicks = 0;
/*
* Get the counter ID stored in file->f_inode->i_private
*/
id = (long)file_inode(file)->i_private;
if (id >= lockevent_num)
return -EBADF;
for_each_possible_cpu(cpu) {
sum += per_cpu(lockevents[id], cpu);
/*
* Need to sum additional counters for some of them
*/
switch (id) {
case LOCKEVENT_pv_latency_kick:
case LOCKEVENT_pv_hash_hops:
kicks += per_cpu(EVENT_COUNT(pv_kick_unlock), cpu);
break;
case LOCKEVENT_pv_latency_wake:
kicks += per_cpu(EVENT_COUNT(pv_kick_wake), cpu);
break;
}
}
if (id == LOCKEVENT_pv_hash_hops) {
u64 frac = 0;
if (kicks) {
frac = 100ULL * do_div(sum, kicks);
frac = DIV_ROUND_CLOSEST_ULL(frac, kicks);
}
/*
* Return a X.XX decimal number
*/
len = snprintf(buf, sizeof(buf) - 1, "%llu.%02llu\n",
sum, frac);
} else {
/*
* Round to the nearest ns
*/
if ((id == LOCKEVENT_pv_latency_kick) ||
(id == LOCKEVENT_pv_latency_wake)) {
if (kicks)
sum = DIV_ROUND_CLOSEST_ULL(sum, kicks);
}
len = snprintf(buf, sizeof(buf) - 1, "%llu\n", sum);
}
return simple_read_from_buffer(user_buf, count, ppos, buf, len);
}
/*
* PV hash hop count
*/
static inline void lockevent_pv_hop(int hopcnt)
{
this_cpu_add(EVENT_COUNT(pv_hash_hops), hopcnt);
}
/*
* Replacement function for pv_kick()
*/
static inline void __pv_kick(int cpu)
{
u64 start = sched_clock();
per_cpu(pv_kick_time, cpu) = start;
pv_kick(cpu);
this_cpu_add(EVENT_COUNT(pv_latency_kick), sched_clock() - start);
}
/*
* Replacement function for pv_wait()
*/
static inline void __pv_wait(u8 *ptr, u8 val)
{
u64 *pkick_time = this_cpu_ptr(&pv_kick_time);
*pkick_time = 0;
pv_wait(ptr, val);
if (*pkick_time) {
this_cpu_add(EVENT_COUNT(pv_latency_wake),
sched_clock() - *pkick_time);
lockevent_inc(pv_kick_wake);
}
}
#define pv_kick(c) __pv_kick(c)
#define pv_wait(p, v) __pv_wait(p, v)
#endif /* CONFIG_PARAVIRT_SPINLOCKS */
#else /* CONFIG_LOCK_EVENT_COUNTS */
static inline void lockevent_pv_hop(int hopcnt) { }
#endif /* CONFIG_LOCK_EVENT_COUNTS */