Before commit: e33a9bba85a8 ("sched/core: move IO scheduling accounting from io_schedule_timeout() into scheduler") delayacct_blkio_end() was called after context-switching into the task which completed I/O. This resulted in double counting: the task would account a delay both waiting for I/O and for time spent in the runqueue. With e33a9bba85a8, delayacct_blkio_end() is called by try_to_wake_up(). In ttwu, we have not yet context-switched. This is more correct, in that the delay accounting ends when the I/O is complete. But delayacct_blkio_end() relies on 'get_current()', and we have not yet context-switched into the task whose I/O completed. This results in the wrong task having its delay accounting statistics updated. Instead of doing that, pass the task_struct being woken to delayacct_blkio_end(), so that it can update the statistics of the correct task.
Unified · Split
| @@ -71,7 +71,7 @@ extern void delayacct_init(void); · 70 unmodified lines | |||
| 71 | extern void __delayacct_tsk_init(struct task_struct *); | 71 | extern void __delayacct_tsk_init(struct task_struct *); |
| 72 | extern void __delayacct_tsk_exit(struct task_struct *); | 72 | extern void __delayacct_tsk_exit(struct task_struct *); |
| 73 | extern void __delayacct_blkio_start(void); | 73 | extern void __delayacct_blkio_start(void); |
| 74 | extern void __delayacct_blkio_end(void); | 74 | extern void __delayacct_blkio_end(struct task_struct *); |
| 75 | extern int __delayacct_add_tsk(struct taskstats *, struct task_struct *); | 75 | extern int __delayacct_add_tsk(struct taskstats *, struct task_struct *); |
| 76 | extern __u64 __delayacct_blkio_ticks(struct task_struct *); | 76 | extern __u64 __delayacct_blkio_ticks(struct task_struct *); |
| 77 | extern void __delayacct_freepages_start(void); | 77 | extern void __delayacct_freepages_start(void); |
| @@ -122,10 +122,10 @@ static inline void delayacct_blkio_start(void) · 44 unmodified lines | |||
| 122 | __delayacct_blkio_start(); | 122 | __delayacct_blkio_start(); |
| 123 | } | 123 | } |
| 124 | 124 | ||
| 125 | static inline void delayacct_blkio_end(void) | 125 | static inline void delayacct_blkio_end(struct task_struct *p) |
| 126 | { | 126 | { |
| 127 | if (current->delays) | 127 | if (current->delays) |
| 128 | __delayacct_blkio_end(); | 128 | __delayacct_blkio_end(p); |
| 129 | delayacct_clear_flag(DELAYACCT_PF_BLKIO); | 129 | delayacct_clear_flag(DELAYACCT_PF_BLKIO); |
| 130 | } | 130 | } |
| 131 | 131 | ||
| @@ -169,7 +169,7 @@ static inline void delayacct_tsk_free(struct task_struct *tsk) · 37 unmodified lines | |||
| 169 | {} | 169 | {} |
| 170 | static inline void delayacct_blkio_start(void) | 170 | static inline void delayacct_blkio_start(void) |
| 171 | {} | 171 | {} |
| 172 | static inline void delayacct_blkio_end(void) | 172 | static inline void delayacct_blkio_end(struct task_struct *p) |
| 173 | {} | 173 | {} |
| 174 | static inline int delayacct_add_tsk(struct taskstats *d, | 174 | static inline int delayacct_add_tsk(struct taskstats *d, |
| 175 | struct task_struct *tsk) | 175 | struct task_struct *tsk) |
| @@ -51,16 +51,16 @@ void __delayacct_tsk_init(struct task_struct *tsk) · 50 unmodified lines | |||
| 51 | * Finish delay accounting for a statistic using its timestamps (@start), | 51 | * Finish delay accounting for a statistic using its timestamps (@start), |
| 52 | * accumalator (@total) and @count | 52 | * accumalator (@total) and @count |
| 53 | */ | 53 | */ |
| 54 | static void delayacct_end(u64 *start, u64 *total, u32 *count) | 54 | static void delayacct_end(spinlock_t *lock, u64 *start, u64 *total, u32 *count) |
| 55 | { | 55 | { |
| 56 | s64 ns = ktime_get_ns() - *start; | 56 | s64 ns = ktime_get_ns() - *start; |
| 57 | unsigned long flags; | 57 | unsigned long flags; |
| 58 | 58 | ||
| 59 | if (ns > 0) { | 59 | if (ns > 0) { |
| 60 | spin_lock_irqsave(¤t->delays->lock, flags); | 60 | spin_lock_irqsave(lock, flags); |
| 61 | *total += ns; | 61 | *total += ns; |
| 62 | (*count)++; | 62 | (*count)++; |
| 63 | spin_unlock_irqrestore(¤t->delays->lock, flags); | 63 | spin_unlock_irqrestore(lock, flags); |
| 64 | } | 64 | } |
| 65 | } | 65 | } |
| 66 | 66 | ||
| @@ -69,17 +69,25 @@ void __delayacct_blkio_start(void) · 2 unmodified lines | |||
| 69 | current->delays->blkio_start = ktime_get_ns(); | 69 | current->delays->blkio_start = ktime_get_ns(); |
| 70 | } | 70 | } |
| 71 | 71 | ||
| 72 | void __delayacct_blkio_end(void) | 72 | /* |
| 73 | * We cannot rely on the `current` macro, as we haven't yet switched back to | ||
| 74 | * the process being woken. | ||
| 75 | */ | ||
| 76 | void __delayacct_blkio_end(struct task_struct *p) | ||
| 73 | { | 77 | { |
| 74 | if (current->delays->flags & DELAYACCT_PF_SWAPIN) | 78 | struct task_delay_info *delays = p->delays; |
| 75 | /* Swapin block I/O */ | 79 | u64 *total; |
| 76 | delayacct_end(¤t->delays->blkio_start, | 80 | u32 *count; |
| 77 | ¤t->delays->swapin_delay, | 81 | |
| 78 | ¤t->delays->swapin_count); | 82 | if (p->delays->flags & DELAYACCT_PF_SWAPIN) { |
| 79 | else /* Other block I/O */ | 83 | total = &delays->swapin_delay; |
| 80 | delayacct_end(¤t->delays->blkio_start, | 84 | count = &delays->swapin_count; |
| 81 | ¤t->delays->blkio_delay, | 85 | } else { |
| 82 | ¤t->delays->blkio_count); | 86 | total = &delays->blkio_delay; |
| 87 | count = &delays->blkio_count; | ||
| 88 | } | ||
| 89 | |||
| 90 | delayacct_end(&delays->lock, &delays->blkio_start, total, count); | ||
| 83 | } | 91 | } |
| 84 | 92 | ||
| 85 | int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk) | 93 | int __delayacct_add_tsk(struct taskstats *d, struct task_struct *tsk) |
| @@ -153,8 +161,10 @@ void __delayacct_freepages_start(void) · 67 unmodified lines | |||
| 153 | 161 | ||
| 154 | void __delayacct_freepages_end(void) | 162 | void __delayacct_freepages_end(void) |
| 155 | { | 163 | { |
| 156 | delayacct_end(¤t->delays->freepages_start, | 164 | delayacct_end( |
| 157 | ¤t->delays->freepages_delay, | 165 | ¤t->delays->lock, |
| 158 | ¤t->delays->freepages_count); | 166 | ¤t->delays->freepages_start, |
| 167 | ¤t->delays->freepages_delay, | ||
| 168 | ¤t->delays->freepages_count); | ||
| 159 | } | 169 | } |
| 160 | 170 | ||
| @@ -2056,7 +2056,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) · 2055 unmodified lines | |||
| 2056 | p->state = TASK_WAKING; | 2056 | p->state = TASK_WAKING; |
| 2057 | 2057 | ||
| 2058 | if (p->in_iowait) { | 2058 | if (p->in_iowait) { |
| 2059 | delayacct_blkio_end(); | 2059 | delayacct_blkio_end(p); |
| 2060 | atomic_dec(&task_rq(p)->nr_iowait); | 2060 | atomic_dec(&task_rq(p)->nr_iowait); |
| 2061 | } | 2061 | } |
| 2062 | 2062 | ||
| @@ -2069,7 +2069,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) · 6 unmodified lines | |||
| 2069 | #else /* CONFIG_SMP */ | 2069 | #else /* CONFIG_SMP */ |
| 2070 | 2070 | ||
| 2071 | if (p->in_iowait) { | 2071 | if (p->in_iowait) { |
| 2072 | delayacct_blkio_end(); | 2072 | delayacct_blkio_end(p); |
| 2073 | atomic_dec(&task_rq(p)->nr_iowait); | 2073 | atomic_dec(&task_rq(p)->nr_iowait); |
| 2074 | } | 2074 | } |
| 2075 | 2075 | ||
| @@ -2122,7 +2122,7 @@ static void try_to_wake_up_local(struct task_struct *p, struct rq_flags *rf) · 46 unmodified lines | |||
| 2122 | 2122 | ||
| 2123 | if (!task_on_rq_queued(p)) { | 2123 | if (!task_on_rq_queued(p)) { |
| 2124 | if (p->in_iowait) { | 2124 | if (p->in_iowait) { |
| 2125 | delayacct_blkio_end(); | 2125 | delayacct_blkio_end(p); |
| 2126 | atomic_dec(&rq->nr_iowait); | 2126 | atomic_dec(&rq->nr_iowait); |
| 2127 | } | 2127 | } |
| 2128 | ttwu_activate(rq, p, ENQUEUE_WAKEUP | ENQUEUE_NOCLOCK); | 2128 | ttwu_activate(rq, p, ENQUEUE_WAKEUP | ENQUEUE_NOCLOCK); |