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bcachefs: Bias reads more in favor of faster device

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Per reports of performance issues on mixed multi device filesystems
where we're issuing too much IO to the spinning rust - tweak this
algorithm.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2024-11-23 16:47:10 -05:00
parent f4d67f6d5a
commit e1cb4f56dc
1 changed files with 8 additions and 0 deletions
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8
fs/bcachefs/extents.c
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@ -89,6 +89,14 @@ static inline bool ptr_better(struct bch_fs *c,
u64 l1 = dev_latency(c, p1.ptr.dev);
u64 l2 = dev_latency(c, p2.ptr.dev);
/*
* Square the latencies, to bias more in favor of the faster
* device - we never want to stop issuing reads to the slower
* device altogether, so that we can update our latency numbers:
*/
l1 *= l1;
l2 *= l2;
/* Pick at random, biased in favor of the faster device: */
return bch2_rand_range(l1 + l2) > l1;