diff options
Diffstat (limited to 'block')
| -rw-r--r-- | block/bfq-iosched.c | 25 | ||||
| -rw-r--r-- | block/bfq-iosched.h | 2 |
2 files changed, 25 insertions, 2 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index aeca22d91101..f0ecd98509d8 100644 --- 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: diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h index 350c39ae2896..ae2f3dadec44 100644 --- a/block/bfq-iosched.h +++ b/block/bfq-iosched.h @@ -499,7 +499,7 @@ struct bfq_data { u64 delta_from_first; /* * Current estimate of the device peak rate, measured in - * [BFQ_RATE_SHIFT * sectors/usec]. The left-shift by + * [(sectors/usec) / 2^BFQ_RATE_SHIFT]. The left-shift by * BFQ_RATE_SHIFT is performed to increase precision in * fixed-point calculations. */ |