diff options
Diffstat (limited to 'block/bfq-iosched.c')
| -rw-r--r-- | block/bfq-iosched.c | 87 |
1 files changed, 41 insertions, 46 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index af1740a1d453..1edac72ab51d 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -752,9 +752,6 @@ static struct kmem_cache *bfq_pool; #define BFQQ_CLOSE_THR (sector_t)(8 * 1024) #define BFQQ_SEEKY(bfqq) (hweight32(bfqq->seek_history) > 32/8) -/* Budget feedback step. */ -#define BFQ_BUDGET_STEP 128 - /* Min samples used for peak rate estimation (for autotuning). */ #define BFQ_PEAK_RATE_SAMPLES 32 @@ -4074,40 +4071,6 @@ static struct bfq_queue *bfq_set_in_service_queue(struct bfq_data *bfqd) return bfqq; } -/* - * bfq_default_budget - return the default budget for @bfqq on @bfqd. - * @bfqd: the device descriptor. - * @bfqq: the queue to consider. - * - * We use 3/4 of the @bfqd maximum budget as the default value - * for the max_budget field of the queues. This lets the feedback - * mechanism to start from some middle ground, then the behavior - * of the process will drive the heuristics towards high values, if - * it behaves as a greedy sequential reader, or towards small values - * if it shows a more intermittent behavior. - */ -static unsigned long bfq_default_budget(struct bfq_data *bfqd, - struct bfq_queue *bfqq) -{ - unsigned long budget; - - /* - * When we need an estimate of the peak rate we need to avoid - * to give budgets that are too short due to previous - * measurements. So, in the first 10 assignments use a - * ``safe'' budget value. For such first assignment the value - * of bfqd->budgets_assigned happens to be lower than 194. - * See __bfq_set_in_service_queue for the formula by which - * this field is computed. - */ - if (bfqd->budgets_assigned < 194 && bfqd->bfq_user_max_budget == 0) - budget = bfq_default_max_budget; - else - budget = bfqd->bfq_max_budget; - - return budget - budget / 4; -} - static void bfq_arm_slice_timer(struct bfq_data *bfqd) { struct bfq_queue *bfqq = bfqd->in_service_queue; @@ -4232,13 +4195,47 @@ static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd, * for throughput. */ case BFQQE_TOO_IDLE: - if (budget > min_budget + BFQ_BUDGET_STEP) - budget -= BFQ_BUDGET_STEP; - else - budget = min_budget; + /* + * This is the only case where we may reduce + * the budget: if there is no request of the + * process still waiting for completion, then + * we assume (tentatively) that the timer has + * expired because the batch of requests of + * the process could have been served with a + * smaller budget. Hence, betting that + * process will behave in the same way when it + * becomes backlogged again, we reduce its + * next budget. As long as we guess right, + * this budget cut reduces the latency + * experienced by the process. + * + * However, if there are still outstanding + * requests, then the process may have not yet + * issued its next request just because it is + * still waiting for the completion of some of + * the still outstanding ones. So in this + * subcase we do not reduce its budget, on the + * contrary we increase it to possibly boost + * the throughput, as discussed in the + * comments to the BUDGET_TIMEOUT case. + */ + if (bfqq->dispatched > 0) /* still outstanding reqs */ + budget = min(budget * 2, bfqd->bfq_max_budget); + else { + if (budget > 5 * min_budget) + budget -= 4 * min_budget; + else + budget = min_budget; + } break; case BFQQE_BUDGET_TIMEOUT: - budget = bfq_default_budget(bfqd, bfqq); + /* + * We double the budget here because it gives + * the chance to boost the throughput if this + * is not a seeky process (and has bumped into + * this timeout because of, e.g., ZBR). + */ + budget = min(budget * 2, bfqd->bfq_max_budget); break; case BFQQE_BUDGET_EXHAUSTED: /* @@ -4250,8 +4247,7 @@ static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd, * definitely increase the budget of this good * candidate to boost the disk throughput. */ - budget = min(budget + 8 * BFQ_BUDGET_STEP, - bfqd->bfq_max_budget); + budget = min(budget * 4, bfqd->bfq_max_budget); break; case BFQQE_NO_MORE_REQUESTS: /* @@ -5025,9 +5021,8 @@ static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq, bfqq->pid = pid; /* Tentative initial value to trade off between thr and lat */ - bfqq->max_budget = bfq_default_budget(bfqd, bfqq); + bfqq->max_budget = (2 * bfq_max_budget(bfqd)) / 3; bfqq->budget_timeout = bfq_smallest_from_now(); - bfqq->pid = pid; /* first request is almost certainly seeky */ bfqq->seek_history = 1; |