diff options
Diffstat (limited to 'block/blk-iolatency.c')
| -rw-r--r-- | block/blk-iolatency.c | 60 |
1 files changed, 45 insertions, 15 deletions
diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c index b0dc4fc64b3e..19923f8a029d 100644 --- a/block/blk-iolatency.c +++ b/block/blk-iolatency.c @@ -69,6 +69,7 @@ #include <linux/module.h> #include <linux/timer.h> #include <linux/memcontrol.h> +#include <linux/sched/loadavg.h> #include <linux/sched/signal.h> #include <trace/events/block.h> #include "blk-rq-qos.h" @@ -126,8 +127,7 @@ struct iolatency_grp { u64 cur_win_nsec; /* total running average of our io latency. */ - u64 total_lat_avg; - u64 total_lat_nr; + u64 lat_avg; /* Our current number of IO's for the last summation. */ u64 nr_samples; @@ -135,6 +135,28 @@ struct iolatency_grp { struct child_latency_info child_lat; }; +#define BLKIOLATENCY_MIN_WIN_SIZE (100 * NSEC_PER_MSEC) +#define BLKIOLATENCY_MAX_WIN_SIZE NSEC_PER_SEC +/* + * These are the constants used to fake the fixed-point moving average + * calculation just like load average. The call to CALC_LOAD folds + * (FIXED_1 (2048) - exp_factor) * new_sample into lat_avg. The sampling + * window size is bucketed to try to approximately calculate average + * latency such that 1/exp (decay rate) is [1 min, 2.5 min) when windows + * elapse immediately. Note, windows only elapse with IO activity. Idle + * periods extend the most recent window. + */ +#define BLKIOLATENCY_NR_EXP_FACTORS 5 +#define BLKIOLATENCY_EXP_BUCKET_SIZE (BLKIOLATENCY_MAX_WIN_SIZE / \ + (BLKIOLATENCY_NR_EXP_FACTORS - 1)) +static const u64 iolatency_exp_factors[BLKIOLATENCY_NR_EXP_FACTORS] = { + 2045, // exp(1/600) - 600 samples + 2039, // exp(1/240) - 240 samples + 2031, // exp(1/120) - 120 samples + 2023, // exp(1/80) - 80 samples + 2014, // exp(1/60) - 60 samples +}; + static inline struct iolatency_grp *pd_to_lat(struct blkg_policy_data *pd) { return pd ? container_of(pd, struct iolatency_grp, pd) : NULL; @@ -462,7 +484,7 @@ static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now) struct child_latency_info *lat_info; struct blk_rq_stat stat; unsigned long flags; - int cpu; + int cpu, exp_idx; blk_rq_stat_init(&stat); preempt_disable(); @@ -480,11 +502,17 @@ static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now) lat_info = &parent->child_lat; - iolat->total_lat_avg = - div64_u64((iolat->total_lat_avg * iolat->total_lat_nr) + - stat.mean, iolat->total_lat_nr + 1); - - iolat->total_lat_nr++; + /* + * CALC_LOAD takes in a number stored in fixed point representation. + * Because we are using this for IO time in ns, the values stored + * are significantly larger than the FIXED_1 denominator (2048). + * Therefore, rounding errors in the calculation are negligible and + * can be ignored. + */ + exp_idx = min_t(int, BLKIOLATENCY_NR_EXP_FACTORS - 1, + div64_u64(iolat->cur_win_nsec, + BLKIOLATENCY_EXP_BUCKET_SIZE)); + CALC_LOAD(iolat->lat_avg, iolatency_exp_factors[exp_idx], stat.mean); /* Everything is ok and we don't need to adjust the scale. */ if (stat.mean <= iolat->min_lat_nsec && @@ -700,8 +728,9 @@ static void iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val) u64 oldval = iolat->min_lat_nsec; iolat->min_lat_nsec = val; - iolat->cur_win_nsec = max_t(u64, val << 4, 100 * NSEC_PER_MSEC); - iolat->cur_win_nsec = min_t(u64, iolat->cur_win_nsec, NSEC_PER_SEC); + iolat->cur_win_nsec = max_t(u64, val << 4, BLKIOLATENCY_MIN_WIN_SIZE); + iolat->cur_win_nsec = min_t(u64, iolat->cur_win_nsec, + BLKIOLATENCY_MAX_WIN_SIZE); if (!oldval && val) atomic_inc(&blkiolat->enabled); @@ -810,14 +839,15 @@ static size_t iolatency_pd_stat(struct blkg_policy_data *pd, char *buf, size_t size) { struct iolatency_grp *iolat = pd_to_lat(pd); - unsigned long long avg_lat = div64_u64(iolat->total_lat_avg, NSEC_PER_USEC); + unsigned long long avg_lat = div64_u64(iolat->lat_avg, NSEC_PER_USEC); + unsigned long long cur_win = div64_u64(iolat->cur_win_nsec, NSEC_PER_MSEC); if (iolat->rq_depth.max_depth == UINT_MAX) - return scnprintf(buf, size, " depth=max avg_lat=%llu", - avg_lat); + return scnprintf(buf, size, " depth=max avg_lat=%llu win=%llu", + avg_lat, cur_win); - return scnprintf(buf, size, " depth=%u avg_lat=%llu", - iolat->rq_depth.max_depth, avg_lat); + return scnprintf(buf, size, " depth=%u avg_lat=%llu win=%llu", + iolat->rq_depth.max_depth, avg_lat, cur_win); } |