Re: [PATCH] avoid using smp_processor_id() in preemptible code (nr_iowait_cpu)

Sergey Senozhatsky
2010-06-15T16:13:03Z

I've changed struct tick_sched to match passed *ts and cpu. Also changed "&per_cpu(tick_cpu_sched, cpu)"
call to "struct tick_sched *tick_get_tick_sched(int cpu)" which we already have.

But I don't really like this part:
struct tick_sched *tick_get_tick_sched(int cpu)
{
struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
ts->cpu = cpu;
^^^^^^^^^^^^^
return ts;
}

Please kindly review.

---

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 52ff8aa..4871ed5 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -137,14 +137,17 @@ static inline int which_bucket(unsigned int duration)
{
int bucket = 0;

+ int cpu = get_cpu();
/*
* We keep two groups of stats; one with no
* IO pending, one without.
* This allows us to calculate
* E(duration)|iowait
*/
- if (nr_iowait_cpu())
+ if (nr_iowait_cpu(cpu))
bucket = BUCKETS/2;
+
+ put_cpu();

if (duration < 10)
return bucket;
@@ -169,14 +172,17 @@ static inline int which_bucket(unsigned int duration)
static inline int performance_multiplier(void)
{
int mult = 1;
-
+ int cpu = get_cpu();
+
/* for higher loadavg, we are more reluctant */

mult += 2 * get_loadavg();

/* for IO wait tasks (per cpu!) we add 5x each */
- mult += 10 * nr_iowait_cpu();
+ mult += 10 * nr_iowait_cpu(cpu);

+ put_cpu();
+
return mult;
}

diff --git a/include/linux/sched.h b/include/linux/sched.h
index f118809..747fcae 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -139,7 +139,7 @@ extern int nr_processes(void);
extern unsigned long nr_running(void);
extern unsigned long nr_uninterruptible(void);
extern unsigned long nr_iowait(void);
-extern unsigned long nr_iowait_cpu(void);
+extern unsigned long nr_iowait_cpu(int cpu);
extern unsigned long this_cpu_load(void);

diff --git a/include/linux/tick.h b/include/linux/tick.h
index b232ccc..db14691 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -51,6 +51,7 @@ struct tick_sched {
unsigned long check_clocks;
enum tick_nohz_mode nohz_mode;
ktime_t idle_tick;
+ int cpu;
int inidle;
int tick_stopped;
unsigned long idle_jiffies;
diff --git a/kernel/sched.c b/kernel/sched.c
index f8b8996..f61b48e 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2864,9 +2864,9 @@ unsigned long nr_iowait(void)
return sum;
}

-unsigned long nr_iowait_cpu(void)
+unsigned long nr_iowait_cpu(int cpu)
{
- struct rq *this = this_rq();
+ struct rq *this = cpu_rq(cpu);
return atomic_read(&this->nr_iowait);
}

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 1d7b9bc..5105345 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -38,7 +38,9 @@ static ktime_t last_jiffies_update;

struct tick_sched *tick_get_tick_sched(int cpu)
{
- return &per_cpu(tick_cpu_sched, cpu);
+ struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ ts->cpu = cpu;
+ return ts;
}

/*
@@ -137,7 +139,7 @@ __setup("nohz=", setup_tick_nohz);
static void tick_nohz_update_jiffies(ktime_t now)
{
int cpu = smp_processor_id();
- struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ struct tick_sched *ts = tick_get_tick_sched(cpu);
unsigned long flags;

cpumask_clear_cpu(cpu, nohz_cpu_mask);
@@ -159,9 +161,10 @@ update_ts_time_stats(struct tick_sched *ts, ktime_t now, u64 *last_update_time)
ktime_t delta;

if (ts->idle_active) {
+ int cpu = ts->cpu;
delta = ktime_sub(now, ts->idle_entrytime);
ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
- if (nr_iowait_cpu() > 0)
+ if (nr_iowait_cpu(cpu) > 0)
ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
ts->idle_entrytime = now;
}
@@ -173,7 +176,7 @@ update_ts_time_stats(struct tick_sched *ts, ktime_t now, u64 *last_update_time)

static void tick_nohz_stop_idle(int cpu, ktime_t now)
{
- struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ struct tick_sched *ts = tick_get_tick_sched(cpu);

update_ts_time_stats(ts, now, NULL);
ts->idle_active = 0;
@@ -211,7 +214,7 @@ static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
*/
u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
{
- struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ struct tick_sched *ts = tick_get_tick_sched(cpu);

if (!tick_nohz_enabled)
return -1;
@@ -237,7 +240,7 @@ EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
*/
u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
{
- struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ struct tick_sched *ts = tick_get_tick_sched(cpu);

if (!tick_nohz_enabled)
return -1;
@@ -267,7 +270,7 @@ void tick_nohz_stop_sched_tick(int inidle)
local_irq_save(flags);

cpu = smp_processor_id();
- ts = &per_cpu(tick_cpu_sched, cpu);
+ ts = tick_get_tick_sched(cpu);

/*
* Call to tick_nohz_start_idle stops the last_update_time from being
@@ -508,7 +511,7 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
void tick_nohz_restart_sched_tick(void)
{
int cpu = smp_processor_id();
- struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ struct tick_sched *ts = tick_get_tick_sched(cpu);
#ifndef CONFIG_VIRT_CPU_ACCOUNTING
unsigned long ticks;
#endif
@@ -671,7 +674,7 @@ static void tick_nohz_kick_tick(int cpu, ktime_t now)
#if 0
/* Switch back to 2.6.27 behaviour */

- struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ struct tick_sched *ts = tick_get_tick_sched(cpu);
ktime_t delta;

/*
@@ -688,7 +691,7 @@ static void tick_nohz_kick_tick(int cpu, ktime_t now)

static inline void tick_check_nohz(int cpu)
{
- struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ struct tick_sched *ts = tick_get_tick_sched(cpu);
ktime_t now;

if (!ts->idle_active && !ts->tick_stopped)
@@ -818,7 +821,7 @@ void tick_setup_sched_timer(void)
#if defined CONFIG_NO_HZ || defined CONFIG_HIGH_RES_TIMERS
void tick_cancel_sched_timer(int cpu)
{
- struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+ struct tick_sched *ts = tick_get_tick_sched(cpu);

# ifdef CONFIG_HIGH_RES_TIMERS
if (ts->sched_timer.base)