+ * (b) Current value of bfqq->soft_rt_next_start. As pointed out
+ * above, greedy applications may happen to meet both the
+ * bandwidth and isochrony requirements under heavy CPU or
+ * storage-device load. In more detail, in these scenarios, these
+ * applications happen, only for limited time periods, to do I/O
+ * slowly enough to meet all the requirements described so far,
+ * including the filtering in above item (a). These slow-speed
+ * time intervals are usually interspersed between other time
+ * intervals during which these applications do I/O at a very high
+ * speed. Fortunately, exactly because of the high speed of the
+ * I/O in the high-speed intervals, the values returned by this
+ * function happen to be so high, near the end of any such
+ * high-speed interval, to be likely to fall *after* the end of
+ * the low-speed time interval that follows. These high values are
+ * stored in bfqq->soft_rt_next_start after each invocation of
+ * this function. As a consequence, if the last value of
+ * bfqq->soft_rt_next_start is constantly used to lower-bound the
+ * next value that this function may return, then, from the very
+ * beginning of a low-speed interval, bfqq->soft_rt_next_start is
+ * likely to be constantly kept so high that any I/O request
+ * issued during the low-speed interval is considered as arriving
+ * to soon for the application to be deemed as soft
+ * real-time. Then, in the high-speed interval that follows, the
+ * application will not be deemed as soft real-time, just because
+ * it will do I/O at a high speed. And so on.
+ *
+ * Getting back to the filtering in item (a), in the following two
+ * cases this filtering might be easily passed by a greedy
+ * application, if the reference quantity was just
+ * bfqd->bfq_slice_idle:
+ * 1) HZ is so low that the duration of a jiffy is comparable to or
+ * higher than bfqd->bfq_slice_idle. This happens, e.g., on slow
+ * devices with HZ=100. The time granularity may be so coarse
+ * that the approximation, in jiffies, of bfqd->bfq_slice_idle
+ * is rather lower than the exact value.