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-rw-r--r--block/blk-iocost.c28
1 files changed, 24 insertions, 4 deletions
diff --git a/block/blk-iocost.c b/block/blk-iocost.c
index 12eefb3d113f..8ac4aad66ebc 100644
--- a/block/blk-iocost.c
+++ b/block/blk-iocost.c
@@ -1539,19 +1539,39 @@ skip_surplus_transfers:
if (rq_wait_pct > RQ_WAIT_BUSY_PCT ||
missed_ppm[READ] > ppm_rthr ||
missed_ppm[WRITE] > ppm_wthr) {
+ /* clearly missing QoS targets, slow down vrate */
ioc->busy_level = max(ioc->busy_level, 0);
ioc->busy_level++;
} else if (rq_wait_pct <= RQ_WAIT_BUSY_PCT * UNBUSY_THR_PCT / 100 &&
missed_ppm[READ] <= ppm_rthr * UNBUSY_THR_PCT / 100 &&
missed_ppm[WRITE] <= ppm_wthr * UNBUSY_THR_PCT / 100) {
- /* take action iff there is contention */
- if (nr_shortages && !nr_lagging) {
+ /* QoS targets are being met with >25% margin */
+ if (nr_shortages) {
+ /*
+ * We're throttling while the device has spare
+ * capacity. If vrate was being slowed down, stop.
+ */
ioc->busy_level = min(ioc->busy_level, 0);
- /* redistribute surpluses first */
- if (!nr_surpluses)
+
+ /*
+ * 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.
+ */
+ if (!nr_lagging && !nr_surpluses)
ioc->busy_level--;
+ } else {
+ /*
+ * Nobody is being throttled and the users aren't
+ * issuing enough IOs to saturate the device. We
+ * simply don't know how close the device is to
+ * saturation. Coast.
+ */
+ ioc->busy_level = 0;
}
} else {
+ /* inside the hysterisis margin, we're good */
ioc->busy_level = 0;
}