diff options
| -rw-r--r-- | block/cfq-iosched.c | 50 |
1 files changed, 32 insertions, 18 deletions
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index bb43a16..15152e2 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -346,14 +346,16 @@ static int cfq_queue_empty(request_queue_t *q) /* * Lifted from AS - choose which of crq1 and crq2 that is best served now. * We choose the request that is closest to the head right now. Distance - * behind the head are penalized and only allowed to a certain extent. + * behind the head is penalized and only allowed to a certain extent. */ static struct cfq_rq * cfq_choose_req(struct cfq_data *cfqd, struct cfq_rq *crq1, struct cfq_rq *crq2) { sector_t last, s1, s2, d1 = 0, d2 = 0; - int r1_wrap = 0, r2_wrap = 0; /* requests are behind the disk head */ unsigned long back_max; +#define CFQ_RQ1_WRAP 0x01 /* request 1 wraps */ +#define CFQ_RQ2_WRAP 0x02 /* request 2 wraps */ + unsigned wrap = 0; /* bit mask: requests behind the disk head? */ if (crq1 == NULL || crq1 == crq2) return crq2; @@ -385,35 +387,47 @@ cfq_choose_req(struct cfq_data *cfqd, struct cfq_rq *crq1, struct cfq_rq *crq2) else if (s1 + back_max >= last) d1 = (last - s1) * cfqd->cfq_back_penalty; else - r1_wrap = 1; + wrap |= CFQ_RQ1_WRAP; if (s2 >= last) d2 = s2 - last; else if (s2 + back_max >= last) d2 = (last - s2) * cfqd->cfq_back_penalty; else - r2_wrap = 1; + wrap |= CFQ_RQ2_WRAP; /* Found required data */ - if (!r1_wrap && r2_wrap) - return crq1; - else if (!r2_wrap && r1_wrap) - return crq2; - else if (r1_wrap && r2_wrap) { - /* both behind the head */ - if (s1 <= s2) + + /* + * By doing switch() on the bit mask "wrap" we avoid having to + * check two variables for all permutations: --> faster! + */ + switch (wrap) { + case 0: /* common case for CFQ: crq1 and crq2 not wrapped */ + if (d1 < d2) return crq1; - else + else if (d2 < d1) return crq2; - } + else { + if (s1 >= s2) + return crq1; + else + return crq2; + } - /* Both requests in front of the head */ - if (d1 < d2) + case CFQ_RQ2_WRAP: return crq1; - else if (d2 < d1) + case CFQ_RQ1_WRAP: return crq2; - else { - if (s1 >= s2) + case (CFQ_RQ1_WRAP|CFQ_RQ2_WRAP): /* both crqs wrapped */ + default: + /* + * Since both rqs are wrapped, + * start with the one that's further behind head + * (--> only *one* back seek required), + * since back seek takes more time than forward. + */ + if (s1 <= s2) return crq1; else return crq2; |
