blk-throttle: set default latency baseline for harddisk
hard disk IO latency varies a lot depending on spindle move. The latency
range could be from several microseconds to several milliseconds. It's
pretty hard to get the baseline latency used by io.low.
We will use a different stragety here. The idea is only using IO with
spindle move to determine if cgroup IO is in good state. For HD, if io
latency is small (< 1ms), we ignore the IO. Such IO is likely from
sequential IO, and is helpless to help determine if a cgroup's IO is
impacted by other cgroups. With this, we only account IO with big
latency. Then we can choose a hardcoded baseline latency for HD (4ms,
which is typical IO latency with seek). With all these settings, the
io.low latency works for both HD and SSD.
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 3b751f7..a7285bf 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -27,6 +27,13 @@
#define MIN_THROTL_IOPS (10)
#define DFL_LATENCY_TARGET (-1L)
#define DFL_IDLE_THRESHOLD (0)
+#define DFL_HD_BASELINE_LATENCY (4000L) /* 4ms */
+#define LATENCY_FILTERED_SSD (0)
+/*
+ * For HD, very small latency comes from sequential IO. Such IO is helpless to
+ * help determine if its IO is impacted by others, hence we ignore the IO
+ */
+#define LATENCY_FILTERED_HD (1000L) /* 1ms */
#define SKIP_LATENCY (((u64)1) << BLK_STAT_RES_SHIFT)
@@ -212,6 +219,7 @@
struct avg_latency_bucket avg_buckets[LATENCY_BUCKET_SIZE];
struct latency_bucket __percpu *latency_buckets;
unsigned long last_calculate_time;
+ unsigned long filtered_latency;
bool track_bio_latency;
};
@@ -2281,7 +2289,7 @@
throtl_track_latency(tg->td, blk_stat_size(&bio->bi_issue_stat),
bio_op(bio), lat);
- if (tg->latency_target) {
+ if (tg->latency_target && lat >= tg->td->filtered_latency) {
int bucket;
unsigned int threshold;
@@ -2417,14 +2425,20 @@
void blk_throtl_register_queue(struct request_queue *q)
{
struct throtl_data *td;
+ int i;
td = q->td;
BUG_ON(!td);
- if (blk_queue_nonrot(q))
+ if (blk_queue_nonrot(q)) {
td->throtl_slice = DFL_THROTL_SLICE_SSD;
- else
+ td->filtered_latency = LATENCY_FILTERED_SSD;
+ } else {
td->throtl_slice = DFL_THROTL_SLICE_HD;
+ td->filtered_latency = LATENCY_FILTERED_HD;
+ for (i = 0; i < LATENCY_BUCKET_SIZE; i++)
+ td->avg_buckets[i].latency = DFL_HD_BASELINE_LATENCY;
+ }
#ifndef CONFIG_BLK_DEV_THROTTLING_LOW
/* if no low limit, use previous default */
td->throtl_slice = DFL_THROTL_SLICE_HD;