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Subject[PATCH] [RFC] CFQ: simplify radix tree lookup in cfq_cic_lookup()
From
Date
0) Not tested and not signed-off.

1) This is to see whether I understand the cfqd->cic_index usage (at
least, part of it).

2) If the lookup of a cic in the radix tree turned up a "dead" cic, then
that cic will be dropped. There's no reason to again try to lookup that
cic: that lookup should return NULL. (If it doesn't return NULL, we seem
to be in trouble.) So there's no need for a do {[...]} while (1) loop
and this code can be simplified a little.
3) Does this make sense?


Paul Bolle
---
block/cfq-iosched.c | 28 +++++++++++++---------------
1 files changed, 13 insertions(+), 15 deletions(-)
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 1f96ad6..0d33d8c 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3120,22 +3120,20 @@ cfq_cic_lookup(struct cfq_data *cfqd, struct io_context *ioc)
return cic;
}

- do {
- cic = radix_tree_lookup(&ioc->radix_root, cfqd->cic_index);
- rcu_read_unlock();
- if (!cic)
- break;
- if (unlikely(cic->key != cfqd)) {
- cfq_drop_dead_cic(cfqd, ioc, cic);
- rcu_read_lock();
- continue;
- }
+ cic = radix_tree_lookup(&ioc->radix_root, cfqd->cic_index);
+ rcu_read_unlock();

- spin_lock_irqsave(&ioc->lock, flags);
- rcu_assign_pointer(ioc->ioc_data, cic);
- spin_unlock_irqrestore(&ioc->lock, flags);
- break;
- } while (1);
+ if (!cic)
+ return NULL;
+
+ if (unlikely(cic->key != cfqd)) {
+ cfq_drop_dead_cic(cfqd, ioc, cic);
+ return NULL;
+ }
+
+ spin_lock_irqsave(&ioc->lock, flags);
+ rcu_assign_pointer(ioc->ioc_data, cic);
+ spin_unlock_irqrestore(&ioc->lock, flags);

return cic;
}
--
1.7.6


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