From 6679a90c4b0dc2563383df1fe0eb170736952a2e Mon Sep 17 00:00:00 2001 From: Shaohua Li Date: Tue, 6 Jun 2017 12:40:43 -0700 Subject: [PATCH] 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 Signed-off-by: Jens Axboe --- block/blk-throttle.c | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-) diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 3b751f706c61..a7285bf2831c 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -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;