pinctrl: at91-pio4: add missing of_node_put

[linux-2.6-block.git] / block / bfq-iosched.c

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index aeca22d911010dc1a11ae9377a46f4ac99b3f629..f0ecd98509d849fd1011b619d6917d9a3da6dd4d 100644 (file)
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -201,7 +201,20 @@ static struct kmem_cache *bfq_pool;
 /* Target observation time interval for a peak-rate update (ns) */
 #define BFQ_RATE_REF_INTERVAL  NSEC_PER_SEC
 
-/* Shift used for peak rate fixed precision calculations. */
+/*
+ * Shift used for peak-rate fixed precision calculations.
+ * With
+ * - the current shift: 16 positions
+ * - the current type used to store rate: u32
+ * - the current unit of measure for rate: [sectors/usec], or, more precisely,
+ *   [(sectors/usec) / 2^BFQ_RATE_SHIFT] to take into account the shift,
+ * the range of rates that can be stored is
+ * [1 / 2^BFQ_RATE_SHIFT, 2^(32 - BFQ_RATE_SHIFT)] sectors/usec =
+ * [1 / 2^16, 2^16] sectors/usec = [15e-6, 65536] sectors/usec =
+ * [15, 65G] sectors/sec
+ * Which, assuming a sector size of 512B, corresponds to a range of
+ * [7.5K, 33T] B/sec
+ */
 #define BFQ_RATE_SHIFT         16
 
 /*
@@ -2637,6 +2650,16 @@ static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq)
        rate /= divisor; /* smoothing constant alpha = 1/divisor */
 
        bfqd->peak_rate += rate;
+
+       /*
+        * For a very slow device, bfqd->peak_rate can reach 0 (see
+        * the minimum representable values reported in the comments
+        * on BFQ_RATE_SHIFT). Push to 1 if this happens, to avoid
+        * divisions by zero where bfqd->peak_rate is used as a
+        * divisor.
+        */
+       bfqd->peak_rate = max_t(u32, 1, bfqd->peak_rate);
+
        update_thr_responsiveness_params(bfqd);
 
 reset_computation: