* When configured for computing the duration of the weight-raising
* for interactive queues automatically (see the comments at the
* beginning of this file), BFQ does it using the following formula:
- * duration = (R / r) * T,
- * where r is the peak rate of the device, and R
- * and T are two reference parameters. In particular,
- * R is the peak rate of the reference device (see below), and
- * T is a reference time: given the systems that are likely
- * to be installed on the reference device according to its speed
- * class, T is about the maximum time needed, under BFQ and
- * while reading two files in parallel, to load typical large
- * applications on these systems (see the comments on
- * max_service_from_wr below, for more details on how T is
- * obtained). In practice, the slower/faster the device at hand is,
- * the more/less it takes to load applications with respect to the
+ * duration = (ref_rate / r) * ref_wr_duration,
+ * where r is the peak rate of the device, and ref_rate and
+ * ref_wr_duration are two reference parameters. In particular,
+ * ref_rate is the peak rate of the reference storage device (see
+ * below), and ref_wr_duration is about the maximum time needed, with
+ * BFQ and while reading two files in parallel, to load typical large
+ * applications on the reference device (see the comments on
+ * max_service_from_wr below, for more details on how ref_wr_duration
+ * is obtained). In practice, the slower/faster the device at hand
+ * is, the more/less it takes to load applications with respect to the
* reference device. Accordingly, the longer/shorter BFQ grants
* weight raising to interactive applications.
*
- * BFQ uses four different reference pairs (R, T), depending on:
- * . whether the device is rotational or non-rotational;
- * . whether the device is slow, such as old or portable HDDs, as well as
- * SD cards, or fast, such as newer HDDs and SSDs.
+ * BFQ uses two different reference pairs (ref_rate, ref_wr_duration),
+ * depending on whether the device is rotational or non-rotational.
*
- * The device's speed class is dynamically (re)detected in
- * bfq_update_peak_rate() every time the estimated peak rate is updated.
+ * In the following definitions, ref_rate[0] and ref_wr_duration[0]
+ * are the reference values for a rotational device, whereas
+ * ref_rate[1] and ref_wr_duration[1] are the reference values for a
+ * non-rotational device. The reference rates are not the actual peak
+ * rates of the devices used as a reference, but slightly lower
+ * values. The reason for using slightly lower values is that the
+ * peak-rate estimator tends to yield slightly lower values than the
+ * actual peak rate (it can yield the actual peak rate only if there
+ * is only one process doing I/O, and the process does sequential
+ * I/O).
*
- * In the following definitions, R_slow[0]/R_fast[0] and
- * T_slow[0]/T_fast[0] are the reference values for a slow/fast
- * rotational device, whereas R_slow[1]/R_fast[1] and
- * T_slow[1]/T_fast[1] are the reference values for a slow/fast
- * non-rotational device. Finally, device_speed_thresh are the
- * thresholds used to switch between speed classes. The reference
- * rates are not the actual peak rates of the devices used as a
- * reference, but slightly lower values. The reason for using these
- * slightly lower values is that the peak-rate estimator tends to
- * yield slightly lower values than the actual peak rate (it can yield
- * the actual peak rate only if there is only one process doing I/O,
- * and the process does sequential I/O).
- *
- * Both the reference peak rates and the thresholds are measured in
- * sectors/usec, left-shifted by BFQ_RATE_SHIFT.
+ * The reference peak rates are measured in sectors/usec, left-shifted
+ * by BFQ_RATE_SHIFT.
*/
-static int R_slow[2] = {1000, 10700};
-static int R_fast[2] = {14000, 33000};
+static int ref_rate[2] = {14000, 33000};
/*
- * To improve readability, a conversion function is used to initialize the
- * following arrays, which entails that they can be initialized only in a
- * function.
+ * To improve readability, a conversion function is used to initialize
+ * the following array, which entails that the array can be
+ * initialized only in a function.
*/
-static int T_slow[2];
-static int T_fast[2];
-static int device_speed_thresh[2];
+static int ref_wr_duration[2];
/*
* BFQ uses the above-detailed, time-based weight-raising mechanism to
if (bfqd->bfq_wr_max_time > 0)
return bfqd->bfq_wr_max_time;
- dur = bfqd->RT_prod;
+ dur = bfqd->rate_dur_prod;
do_div(dur, bfqd->peak_rate);
/*
/*
* Update parameters related to throughput and responsiveness, as a
* function of the estimated peak rate. See comments on
- * bfq_calc_max_budget(), and on T_slow and T_fast arrays.
+ * bfq_calc_max_budget(), and on the ref_wr_duration array.
*/
static void update_thr_responsiveness_params(struct bfq_data *bfqd)
{
- int dev_type = blk_queue_nonrot(bfqd->queue);
-
- if (bfqd->bfq_user_max_budget == 0)
+ if (bfqd->bfq_user_max_budget == 0) {
bfqd->bfq_max_budget =
bfq_calc_max_budget(bfqd);
-
- if (bfqd->device_speed == BFQ_BFQD_FAST &&
- bfqd->peak_rate < device_speed_thresh[dev_type]) {
- bfqd->device_speed = BFQ_BFQD_SLOW;
- bfqd->RT_prod = R_slow[dev_type] *
- T_slow[dev_type];
- } else if (bfqd->device_speed == BFQ_BFQD_SLOW &&
- bfqd->peak_rate > device_speed_thresh[dev_type]) {
- bfqd->device_speed = BFQ_BFQD_FAST;
- bfqd->RT_prod = R_fast[dev_type] *
- T_fast[dev_type];
+ bfq_log(bfqd, "new max_budget = %d", bfqd->bfq_max_budget);
}
-
- bfq_log(bfqd,
-"dev_type %s dev_speed_class = %s (%llu sects/sec), thresh %llu setcs/sec",
- dev_type == 0 ? "ROT" : "NONROT",
- bfqd->device_speed == BFQ_BFQD_FAST ? "FAST" : "SLOW",
- bfqd->device_speed == BFQ_BFQD_FAST ?
- (USEC_PER_SEC*(u64)R_fast[dev_type])>>BFQ_RATE_SHIFT :
- (USEC_PER_SEC*(u64)R_slow[dev_type])>>BFQ_RATE_SHIFT,
- (USEC_PER_SEC*(u64)device_speed_thresh[dev_type])>>
- BFQ_RATE_SHIFT);
}
static void bfq_reset_rate_computation(struct bfq_data *bfqd,
bfqd->wr_busy_queues = 0;
/*
- * Begin by assuming, optimistically, that the device is a
- * high-speed one, and that its peak rate is equal to 2/3 of
- * the highest reference rate.
+ * Begin by assuming, optimistically, that the device peak
+ * rate is equal to 2/3 of the highest reference rate.
*/
- bfqd->RT_prod = R_fast[blk_queue_nonrot(bfqd->queue)] *
- T_fast[blk_queue_nonrot(bfqd->queue)];
- bfqd->peak_rate = R_fast[blk_queue_nonrot(bfqd->queue)] * 2 / 3;
- bfqd->device_speed = BFQ_BFQD_FAST;
+ bfqd->rate_dur_prod = ref_rate[blk_queue_nonrot(bfqd->queue)] *
+ ref_wr_duration[blk_queue_nonrot(bfqd->queue)];
+ bfqd->peak_rate = ref_rate[blk_queue_nonrot(bfqd->queue)] * 2 / 3;
spin_lock_init(&bfqd->lock);
/*
* Times to load large popular applications for the typical
* systems installed on the reference devices (see the
- * comments before the definitions of the next two
- * arrays). Actually, we use slightly slower values, as the
+ * comments before the definition of the next
+ * array). Actually, we use slightly lower values, as the
* estimated peak rate tends to be smaller than the actual
* peak rate. The reason for this last fact is that estimates
* are computed over much shorter time intervals than the long
* scheduler cannot rely on a peak-rate-evaluation workload to
* be run for a long time.
*/
- T_slow[0] = msecs_to_jiffies(3500); /* actually 4 sec */
- T_slow[1] = msecs_to_jiffies(6000); /* actually 6.5 sec */
- T_fast[0] = msecs_to_jiffies(7000); /* actually 8 sec */
- T_fast[1] = msecs_to_jiffies(2500); /* actually 3 sec */
-
- /*
- * Thresholds that determine the switch between speed classes
- * (see the comments before the definition of the array
- * device_speed_thresh). These thresholds are biased towards
- * transitions to the fast class. This is safer than the
- * opposite bias. In fact, a wrong transition to the slow
- * class results in short weight-raising periods, because the
- * speed of the device then tends to be higher that the
- * reference peak rate. On the opposite end, a wrong
- * transition to the fast class tends to increase
- * weight-raising periods, because of the opposite reason.
- */
- device_speed_thresh[0] = (4 * R_slow[0]) / 3;
- device_speed_thresh[1] = (4 * R_slow[1]) / 3;
+ ref_wr_duration[0] = msecs_to_jiffies(7000); /* actually 8 sec */
+ ref_wr_duration[1] = msecs_to_jiffies(2500); /* actually 3 sec */
ret = elv_register(&iosched_bfq_mq);
if (ret)
projects / linux-2.6-block.git / blobdiff