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Commit 6679a90c authored by Shaohua Li's avatar Shaohua Li Committed by Jens Axboe
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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: default avatarShaohua Li <shli@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent a41b816c

block/blk-throttle.c

+17 −3
Original line number Diff line number Diff line
@@ -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;