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Reduced caching during rbyd lookup based on preliminary benchmarking

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This deserves more scrutiny in the future, but early benchmarking shows
caching here to add significant cost, since we often load branches we
don't take.

There may be smarter things we can do, but ideas quickly get into
branch-prediction territory, which is very, very out of scope.
This commit is contained in:
Christopher Haster
2023-01-20 13:09:12 -06:00
parent 0eccd6515f
commit 22f00649a6
1 changed files with 3 additions and 5 deletions
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lfs.c
+3 -5
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@@ -126,7 +126,7 @@ static int lfs_bd_read(lfs_t *lfs,
rcache->off = lfs_aligndown(off, lfs->cfg->read_size);
rcache->size = lfs_min(
lfs_min(
lfs_alignup(off+hint, lfs->cfg->read_size),
lfs_alignup(off+lfs_max(size, hint), lfs->cfg->read_size),
lfs->cfg->block_size)
- rcache->off,
lfs->cfg->cache_size);
@@ -1313,7 +1313,7 @@ static lfsr_stag_t lfsr_rbyd_lookup(lfs_t *lfs, const lfsr_rbyd_t *rbyd,
lfsr_tag_t alt;
lfs_off_t jump;
lfs_ssize_t delta = lfsr_rbyd_readtag(lfs,
&lfs->pcache, &lfs->rcache, lfs->cfg->block_size,
&lfs->pcache, &lfs->rcache, 0,
rbyd->block, branch, &alt, &jump, NULL);
if (delta < 0) {
return delta;
@@ -1350,7 +1350,6 @@ static lfsr_stag_t lfsr_rbyd_lookup(lfs_t *lfs, const lfsr_rbyd_t *rbyd,
if (size) {
*size = jump;
}
return tag_;
}
}
@@ -1371,7 +1370,6 @@ static lfs_ssize_t lfsr_rbyd_get(lfs_t *lfs, const lfsr_rbyd_t *rbyd,
return LFS_ERR_NOENT;
}
// note that it's highly likely the data is in our cache now
lfs_size_t delta = lfs_min(size, size_);
int err = lfs_bd_read(lfs,
&lfs->pcache, &lfs->rcache, delta,
@@ -1631,7 +1629,7 @@ static int lfsr_rbyd_append(lfs_t *lfs, lfsr_rbyd_t *rbyd_,
lfsr_tag_t alt;
lfs_off_t jump;
lfs_ssize_t delta = lfsr_rbyd_readtag(lfs,
&lfs->pcache, &lfs->rcache, lfs->cfg->block_size,
&lfs->pcache, &lfs->rcache, 0,
rbyd_->block, lower_branch, &alt, &jump, NULL);
if (delta < 0) {
return delta;