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From 3e2bdd6dff239afd8386e8758eee69ad61e5a3d6 Mon Sep 17 00:00:00 2001 |
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From: Paolo Valente <paolo.valente@linaro.org> |
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Date: Thu, 21 Sep 2017 11:04:01 +0200 |
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Subject: [PATCH] block, bfq: check and switch back to interactive wr also on |
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queue split |
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|
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As already explained in the message of commit "block, bfq: fix |
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wrong init of saved start time for weight raising", if a soft |
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real-time weight-raising period happens to be nested in a larger |
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interactive weight-raising period, then BFQ restores the interactive |
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weight raising at the end of the soft real-time weight raising. In |
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particular, BFQ checks whether the latter has ended only on request |
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dispatches. |
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|
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Unfortunately, the above scheme fails to restore interactive weight |
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raising in the following corner case: if a bfq_queue, say Q, |
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1) Is merged with another bfq_queue while it is in a nested soft |
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real-time weight-raising period. The weight-raising state of Q is |
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then saved, and not considered any longer until a split occurs. |
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2) Is split from the other bfq_queue(s) at a time instant when its |
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soft real-time weight raising is already finished. |
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On the split, while resuming the previous, soft real-time |
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weight-raised state of the bfq_queue Q, BFQ checks whether the |
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current soft real-time weight-raising period is actually over. If so, |
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BFQ switches weight raising off for Q, *without* checking whether the |
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soft real-time period was actually nested in a non-yet-finished |
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interactive weight-raising period. |
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|
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This commit addresses this issue by adding the above missing check in |
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bfq_queue splits, and restoring interactive weight raising if needed. |
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|
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Signed-off-by: Paolo Valente <paolo.valente@linaro.org> |
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Tested-by: Angelo Ruocco <angeloruocco90@gmail.com> |
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Tested-by: Mirko Montanari <mirkomontanari91@gmail.com> |
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Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name> |
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Tested-by: Lee Tibbert <lee.tibbert@gmail.com> |
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Signed-off-by: Jens Axboe <axboe@kernel.dk> |
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--- |
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block/bfq-iosched.c | 87 ++++++++++++++++++++++++++++++----------------------- |
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1 file changed, 49 insertions(+), 38 deletions(-) |
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|
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diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c |
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index c25955c25e03..33b63bc4a64b 100644 |
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--- a/block/bfq-iosched.c |
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+++ b/block/bfq-iosched.c |
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@@ -724,6 +724,44 @@ static void bfq_updated_next_req(struct bfq_data *bfqd, |
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} |
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} |
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|
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+static unsigned int bfq_wr_duration(struct bfq_data *bfqd) |
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+{ |
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+ u64 dur; |
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+ |
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+ if (bfqd->bfq_wr_max_time > 0) |
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+ return bfqd->bfq_wr_max_time; |
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+ |
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+ dur = bfqd->RT_prod; |
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+ do_div(dur, bfqd->peak_rate); |
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+ |
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+ /* |
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+ * Limit duration between 3 and 13 seconds. Tests show that |
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+ * higher values than 13 seconds often yield the opposite of |
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+ * the desired result, i.e., worsen responsiveness by letting |
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+ * non-interactive and non-soft-real-time applications |
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+ * preserve weight raising for a too long time interval. |
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+ * |
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+ * On the other end, lower values than 3 seconds make it |
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+ * difficult for most interactive tasks to complete their jobs |
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+ * before weight-raising finishes. |
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+ */ |
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+ if (dur > msecs_to_jiffies(13000)) |
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+ dur = msecs_to_jiffies(13000); |
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+ else if (dur < msecs_to_jiffies(3000)) |
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+ dur = msecs_to_jiffies(3000); |
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+ |
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+ return dur; |
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+} |
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+ |
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+/* switch back from soft real-time to interactive weight raising */ |
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+static void switch_back_to_interactive_wr(struct bfq_queue *bfqq, |
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+ struct bfq_data *bfqd) |
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+{ |
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+ bfqq->wr_coeff = bfqd->bfq_wr_coeff; |
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+ bfqq->wr_cur_max_time = bfq_wr_duration(bfqd); |
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+ bfqq->last_wr_start_finish = bfqq->wr_start_at_switch_to_srt; |
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+} |
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+ |
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static void |
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bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd, |
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struct bfq_io_cq *bic, bool bfq_already_existing) |
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@@ -750,10 +788,16 @@ bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd, |
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if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) || |
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time_is_before_jiffies(bfqq->last_wr_start_finish + |
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bfqq->wr_cur_max_time))) { |
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- bfq_log_bfqq(bfqq->bfqd, bfqq, |
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- "resume state: switching off wr"); |
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- |
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- bfqq->wr_coeff = 1; |
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+ if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time && |
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+ !bfq_bfqq_in_large_burst(bfqq) && |
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+ time_is_after_eq_jiffies(bfqq->wr_start_at_switch_to_srt + |
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+ bfq_wr_duration(bfqd))) { |
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+ switch_back_to_interactive_wr(bfqq, bfqd); |
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+ } else { |
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+ bfqq->wr_coeff = 1; |
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+ bfq_log_bfqq(bfqq->bfqd, bfqq, |
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+ "resume state: switching off wr"); |
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+ } |
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} |
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|
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/* make sure weight will be updated, however we got here */ |
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@@ -1173,35 +1217,6 @@ static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd, |
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return wr_or_deserves_wr; |
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} |
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|
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-static unsigned int bfq_wr_duration(struct bfq_data *bfqd) |
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-{ |
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- u64 dur; |
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- |
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- if (bfqd->bfq_wr_max_time > 0) |
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- return bfqd->bfq_wr_max_time; |
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- |
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- dur = bfqd->RT_prod; |
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- do_div(dur, bfqd->peak_rate); |
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- |
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- /* |
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- * Limit duration between 3 and 13 seconds. Tests show that |
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- * higher values than 13 seconds often yield the opposite of |
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- * the desired result, i.e., worsen responsiveness by letting |
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- * non-interactive and non-soft-real-time applications |
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- * preserve weight raising for a too long time interval. |
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- * |
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- * On the other end, lower values than 3 seconds make it |
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- * difficult for most interactive tasks to complete their jobs |
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- * before weight-raising finishes. |
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- */ |
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- if (dur > msecs_to_jiffies(13000)) |
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- dur = msecs_to_jiffies(13000); |
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- else if (dur < msecs_to_jiffies(3000)) |
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- dur = msecs_to_jiffies(3000); |
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- |
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- return dur; |
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-} |
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- |
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/* |
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* Return the farthest future time instant according to jiffies |
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* macros. |
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@@ -3501,11 +3516,7 @@ static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq) |
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bfq_wr_duration(bfqd))) |
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bfq_bfqq_end_wr(bfqq); |
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else { |
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- /* switch back to interactive wr */ |
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- bfqq->wr_coeff = bfqd->bfq_wr_coeff; |
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- bfqq->wr_cur_max_time = bfq_wr_duration(bfqd); |
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- bfqq->last_wr_start_finish = |
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- bfqq->wr_start_at_switch_to_srt; |
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+ switch_back_to_interactive_wr(bfqq, bfqd); |
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bfqq->entity.prio_changed = 1; |
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} |
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} |
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-- |
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2.15.1 |
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