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-rw-r--r--block/blk-iolatency.c60
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);
}