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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>
This commit is contained in:
Shaohua Li 2017-06-06 12:40:43 -07:00 committed by Jens Axboe
parent a41b816c17
commit 6679a90c4b
1 changed files with 17 additions and 3 deletions
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20
block/blk-throttle.c
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@ -27,6 +27,13 @@ static int throtl_quantum = 32;
#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 throtl_data
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 @@ void blk_throtl_bio_endio(struct bio *bio)
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_exit(struct request_queue *q)
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;