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Reduced ctz traverse runtime by 2x

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Unfortunately for us, the ctz skip-list does not offer very much benefit
for full traversals. Since the information about which blocks are in
use are spread throughout the file, we can't use the fast-lanes
embedded in the skip-list without missing blocks.

However, it turns out we can at least use the 2nd level of the skip-list
without missing any blocks. From an asymptotic analysis, a constant speed
up isn't interesting, but from a pragmatic perspective, a 2x speedup is
not bad.
This commit is contained in:
Christopher Haster
2017-12-27 12:30:01 -06:00
parent db8872781a
commit 1fb6a19520
1 changed files with 12 additions and 2 deletions
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14
lfs.c
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@ -1195,12 +1195,22 @@ static int lfs_ctz_traverse(lfs_t *lfs,
return 0;
}
err = lfs_cache_read(lfs, rcache, pcache, head, 0, &head, 4);
lfs_block_t heads[2];
int count = 2 - (index & 1);
err = lfs_cache_read(lfs, rcache, pcache, head, 0, &heads, count*4);
if (err) {
return err;
}
index -= 1;
for (int i = 0; i < count-1; i++) {
err = cb(data, heads[i]);
if (err) {
return err;
}
}
head = heads[count-1];
index -= count;
}
}