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Differential D50389

pctrie: use popmap in locked lookup_range
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Authored by dougm on Sat, May 17, 5:44 AM.
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alc
markj
kib
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rG6fd6c29a236c: pctrie: use popmap in locked lookup_range
Summary

When lookup_range is invoked with a lock held, the popmap field of a level-0 parent node can be used to find the next null child (if any) of that parent, allowing null checks to be removed from the loop and for the compiler to perform some loop unrolling.

Test Plan

A test ran buildworlds repeatedly, and counted calls to lookup_range for both the (locked) iterator version and the unlocked version. Performance for the locked version improved very slightly.

Original:
iter_calls: 4429708 61.276887325304514
iter_calls: 4154212 59.70931430557709
iter_calls: 4150022 60.694023549754675
iter_calls: 4150131 60.67953228464354

unlocked_calls: 840221 321.7100846086922
unlocked_calls: 782491 315.57590183145874
unlocked_calls: 783626 329.88843147113545
unlocked_calls: 786474 333.208179799968

Modified:
iter_calls: 4421212 60.891263300651495
iter_calls: 4157109 59.29220956198166
iter_calls: 4151355 59.99452805168433
iter_calls: 4151863 59.19281801928435

unlocked_calls: 839892 304.41711672453124
unlocked_calls: 781278 325.4182877285678
unlocked_calls: 781892 326.2977495613205
unlocked_calls: 781495 320.9273175132279

Diff Detail

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Event Timeline

dougm requested review of this revision.Sat, May 17, 5:44 AM
dougm created this revision.
markj added a comment.Sat, May 17, 2:38 PM

vm_page: use popmap in locked lookup_range

pctrie: ... would seem to make more sense as a commit title.

sys/kern/subr_pctrie.c
633–653
dougm updated this revision to Diff 155616.Sat, May 17, 4:43 PM
dougm marked an inline comment as done.
dougm retitled this revision from vm_page: use popmap in locked lookup_range to pctrie: use popmap in locked lookup_range.
kib added inline comments.Sat, May 17, 6:14 PM
sys/kern/subr_pctrie.c
658

Why do you continue the fill for PCTRIE_LOCKED case ? Isn't it results in NULL slots in value[]?

dougm added inline comments.Sat, May 17, 6:31 PM
sys/kern/subr_pctrie.c
658

In the PCTRIE_LOCKED case, I know that val is not NULL, because I computed end to make sure that the iteration stopped before reaching the first NULL.

kib added inline comments.Sat, May 17, 6:33 PM
sys/kern/subr_pctrie.c
658

Assert that, and explain in comment, please?

dougm updated this revision to Diff 155619.Sat, May 17, 6:55 PM

Add comments to explain end calculation. Add KASSERT to check that copied pages are not NULL.

dougm updated this revision to Diff 155620.Sat, May 17, 7:22 PM

Remove extra paren on KASSERT.

dougm updated this revision to Diff 155623.Sat, May 17, 7:45 PM

Correct ',' to '.' in comment.

kib accepted this revision.Sat, May 17, 7:56 PM
This revision is now accepted and ready to land.Sat, May 17, 7:56 PM
dougm updated this revision to Diff 155624.Sat, May 17, 7:56 PM

@alc asks for a more commenting about why this code treats SMR and locked diferently. I oblige.

This revision now requires review to proceed.Sat, May 17, 7:56 PM
alc accepted this revision.Sat, May 17, 10:00 PM
alc added inline comments.
sys/kern/subr_pctrie.c
635
645
This revision is now accepted and ready to land.Sat, May 17, 10:00 PM
Closed by commit rG6fd6c29a236c: pctrie: use popmap in locked lookup_range (authored by dougm). · Explain WhySun, May 18, 3:14 AM
This revision was automatically updated to reflect the committed changes.
dougm marked 2 inline comments as done.
dougm added a commit: rG6fd6c29a236c: pctrie: use popmap in locked lookup_range.
Herald added subscribers: olce, imp. · View Herald TranscriptSun, May 18, 3:14 AM

Revision Contents
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sys/
kern/
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Diff 155624

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sys/kern/subr_pctrie.c

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