From 56d9912106b0974ffb6dd264c80c7e816677e998 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Wed, 11 May 2011 14:27:03 +1000 Subject: md: simplify raid10 read_balance raid10 read balance has two different loop for looking through possible devices to chose the best. Collapse those into one loop and generally make the code more readable. Signed-off-by: NeilBrown --- drivers/md/raid10.c | 110 +++++++++++++++++++++------------------------------- 1 file changed, 44 insertions(+), 66 deletions(-) diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c index 8e9462626ec5..8ea0acad606b 100644 --- a/drivers/md/raid10.c +++ b/drivers/md/raid10.c @@ -488,13 +488,19 @@ static int raid10_mergeable_bvec(struct request_queue *q, static int read_balance(conf_t *conf, r10bio_t *r10_bio) { const sector_t this_sector = r10_bio->sector; - int disk, slot, nslot; + int disk, slot; const int sectors = r10_bio->sectors; - sector_t new_distance, current_distance; + sector_t new_distance, best_dist; mdk_rdev_t *rdev; + int do_balance; + int best_slot; raid10_find_phys(conf, r10_bio); rcu_read_lock(); +retry: + best_slot = -1; + best_dist = MaxSector; + do_balance = 1; /* * Check if we can balance. We can balance on the whole * device if no resync is going on (recovery is ok), or below @@ -502,86 +508,58 @@ static int read_balance(conf_t *conf, r10bio_t *r10_bio) * above the resync window. */ if (conf->mddev->recovery_cp < MaxSector - && (this_sector + sectors >= conf->next_resync)) { - /* make sure that disk is operational */ - slot = 0; - disk = r10_bio->devs[slot].devnum; - - while ((rdev = rcu_dereference(conf->mirrors[disk].rdev)) == NULL || - r10_bio->devs[slot].bio == IO_BLOCKED || - !test_bit(In_sync, &rdev->flags)) { - slot++; - if (slot == conf->copies) { - slot = 0; - disk = -1; - break; - } - disk = r10_bio->devs[slot].devnum; - } - goto rb_out; - } - + && (this_sector + sectors >= conf->next_resync)) + do_balance = 0; - /* make sure the disk is operational */ - slot = 0; - disk = r10_bio->devs[slot].devnum; - while ((rdev=rcu_dereference(conf->mirrors[disk].rdev)) == NULL || - r10_bio->devs[slot].bio == IO_BLOCKED || - !test_bit(In_sync, &rdev->flags)) { - slot ++; - if (slot == conf->copies) { - disk = -1; - goto rb_out; - } + for (slot = 0; slot < conf->copies ; slot++) { + if (r10_bio->devs[slot].bio == IO_BLOCKED) + continue; disk = r10_bio->devs[slot].devnum; - } - - - current_distance = abs(r10_bio->devs[slot].addr - - conf->mirrors[disk].head_position); - - /* Find the disk whose head is closest, - * or - for far > 1 - find the closest to partition beginning */ - - for (nslot = slot; nslot < conf->copies; nslot++) { - int ndisk = r10_bio->devs[nslot].devnum; - - - if ((rdev=rcu_dereference(conf->mirrors[ndisk].rdev)) == NULL || - r10_bio->devs[nslot].bio == IO_BLOCKED || - !test_bit(In_sync, &rdev->flags)) + rdev = rcu_dereference(conf->mirrors[disk].rdev); + if (rdev == NULL) + continue; + if (!test_bit(In_sync, &rdev->flags)) continue; + if (!do_balance) + break; + /* This optimisation is debatable, and completely destroys * sequential read speed for 'far copies' arrays. So only * keep it for 'near' arrays, and review those later. */ - if (conf->near_copies > 1 && !atomic_read(&rdev->nr_pending)) { - disk = ndisk; - slot = nslot; + if (conf->near_copies > 1 && !atomic_read(&rdev->nr_pending)) break; - } /* for far > 1 always use the lowest address */ if (conf->far_copies > 1) - new_distance = r10_bio->devs[nslot].addr; + new_distance = r10_bio->devs[slot].addr; else - new_distance = abs(r10_bio->devs[nslot].addr - - conf->mirrors[ndisk].head_position); - if (new_distance < current_distance) { - current_distance = new_distance; - disk = ndisk; - slot = nslot; + new_distance = abs(r10_bio->devs[slot].addr - + conf->mirrors[disk].head_position); + if (new_distance < best_dist) { + best_dist = new_distance; + best_slot = slot; } } + if (slot == conf->copies) + slot = best_slot; -rb_out: - r10_bio->read_slot = slot; -/* conf->next_seq_sect = this_sector + sectors;*/ - - if (disk >= 0 && (rdev=rcu_dereference(conf->mirrors[disk].rdev))!= NULL) - atomic_inc(&conf->mirrors[disk].rdev->nr_pending); - else + if (slot >= 0) { + disk = r10_bio->devs[slot].devnum; + rdev = rcu_dereference(conf->mirrors[disk].rdev); + if (!rdev) + goto retry; + atomic_inc(&rdev->nr_pending); + if (test_bit(Faulty, &rdev->flags)) { + /* Cannot risk returning a device that failed + * before we inc'ed nr_pending + */ + rdev_dec_pending(rdev, conf->mddev); + goto retry; + } + r10_bio->read_slot = slot; + } else disk = -1; rcu_read_unlock(); -- cgit v1.2.3