Commit 065655c8 authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

blk-iocost: decouple vrate adjustment from surplus transfers 



Budget donations are inaccurate and could take multiple periods to converge.
To prevent triggering vrate adjustments while surplus transfers were
catching up, vrate adjustment was suppressed if donations were increasing,
which was indicated by non-zero nr_surpluses.

This entangling won't be necessary with the scheduled rewrite of donation
mechanism which will make it precise and immediate. Let's decouple the two
in preparation.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 8692d2db

block/blk-iocost.c

+7 −12
Original line number Diff line number Diff line
@@ -1508,7 +1508,7 @@ static void ioc_timer_fn(struct timer_list *timer) 
	struct ioc_gq *iocg, *tiocg;

	struct ioc_now now;

	LIST_HEAD(surpluses);

	int nr_surpluses = 0, nr_shortages = 0, nr_lagging = 0;

	int nr_shortages = 0, nr_lagging = 0;

	u32 ppm_rthr = MILLION - ioc->params.qos[QOS_RPPM];

	u32 ppm_wthr = MILLION - ioc->params.qos[QOS_WPPM];

	u32 missed_ppm[2], rq_wait_pct;
@@ -1640,10 +1640,8 @@ static void ioc_timer_fn(struct timer_list *timer) 
			atomic64_add(delta, &iocg->vtime);

			atomic64_add(delta, &iocg->done_vtime);

			/* if usage is sufficiently low, maybe it can donate */

			if (surplus_adjusted_hweight_inuse(usage, hw_inuse)) {

			if (surplus_adjusted_hweight_inuse(usage, hw_inuse))

				list_add(&iocg->surplus_list, &surpluses);

				nr_surpluses++;

			}

		} else if (hw_inuse < hw_active) {

			u32 new_hwi, new_inuse;
@@ -1673,7 +1671,7 @@ static void ioc_timer_fn(struct timer_list *timer) 
		}

	}



	if (!nr_shortages || !nr_surpluses)

	if (!nr_shortages || list_empty(&surpluses))

		goto skip_surplus_transfers;



	/* there are both shortages and surpluses, transfer surpluses */
@@ -1738,11 +1736,9 @@ skip_surplus_transfers: 


			/*

			 * If there are IOs spanning multiple periods, wait

			 * them out before pushing the device harder.  If

			 * there are surpluses, let redistribution work it

			 * out first.

			 * them out before pushing the device harder.

			 */

			if (!nr_lagging && !nr_surpluses)

			if (!nr_lagging)

				ioc->busy_level--;

		} else {

			/*
@@ -1796,15 +1792,14 @@ skip_surplus_transfers: 
		}



		trace_iocost_ioc_vrate_adj(ioc, vrate, missed_ppm, rq_wait_pct,

					   nr_lagging, nr_shortages,

					   nr_surpluses);

					   nr_lagging, nr_shortages);



		atomic64_set(&ioc->vtime_rate, vrate);

		ioc_refresh_margins(ioc);

	} else if (ioc->busy_level != prev_busy_level || nr_lagging) {

		trace_iocost_ioc_vrate_adj(ioc, atomic64_read(&ioc->vtime_rate),

					   missed_ppm, rq_wait_pct, nr_lagging,

					   nr_shortages, nr_surpluses);

					   nr_shortages);

	}



	ioc_refresh_params(ioc, false);

include/trace/events/iocost.h

+4 −9
Original line number Diff line number Diff line
@@ -128,11 +128,9 @@ DEFINE_EVENT(iocg_inuse_update, iocost_inuse_reset, 
TRACE_EVENT(iocost_ioc_vrate_adj,



	TP_PROTO(struct ioc *ioc, u64 new_vrate, u32 *missed_ppm,

		u32 rq_wait_pct, int nr_lagging, int nr_shortages,

		int nr_surpluses),

		u32 rq_wait_pct, int nr_lagging, int nr_shortages),



	TP_ARGS(ioc, new_vrate, missed_ppm, rq_wait_pct, nr_lagging, nr_shortages,

		nr_surpluses),

	TP_ARGS(ioc, new_vrate, missed_ppm, rq_wait_pct, nr_lagging, nr_shortages),



	TP_STRUCT__entry (

		__string(devname, ioc_name(ioc))
@@ -144,7 +142,6 @@ TRACE_EVENT(iocost_ioc_vrate_adj, 
		__field(u32, rq_wait_pct)

		__field(int, nr_lagging)

		__field(int, nr_shortages)

		__field(int, nr_surpluses)

	),



	TP_fast_assign(
@@ -157,15 +154,13 @@ TRACE_EVENT(iocost_ioc_vrate_adj, 
		__entry->rq_wait_pct = rq_wait_pct;

		__entry->nr_lagging = nr_lagging;

		__entry->nr_shortages = nr_shortages;

		__entry->nr_surpluses = nr_surpluses;

	),



	TP_printk("[%s] vrate=%llu->%llu busy=%d missed_ppm=%u:%u rq_wait_pct=%u lagging=%d shortages=%d surpluses=%d",

	TP_printk("[%s] vrate=%llu->%llu busy=%d missed_ppm=%u:%u rq_wait_pct=%u lagging=%d shortages=%d",

		__get_str(devname), __entry->old_vrate, __entry->new_vrate,

		__entry->busy_level,

		__entry->read_missed_ppm, __entry->write_missed_ppm,

		__entry->rq_wait_pct, __entry->nr_lagging, __entry->nr_shortages,

		__entry->nr_surpluses

		__entry->rq_wait_pct, __entry->nr_lagging, __entry->nr_shortages

	)

);

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