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Differential D17063

depessimize copyinstr_smap
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Authored by mjg on Sep 6 2018, 5:05 PM.
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kib
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rS338508: amd64: depessimize copyinstr_smap
Summary

It was showing up on a name resolution-heavy benchmark (4% as reported by pmcstat, 0.7% after the patch).

The main reason was the slac/clac combo around each byte copy.

The patch reoders lables to remove a common case forward jump (the nosmap routine still suffers it) and englarges the smap-disabled region.

Note the current byte copy loop is still slow and is subject to being optimized later.

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rS FreeBSD src repository - subversion
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Event Timeline

mjg created this revision.Sep 6 2018, 5:05 PM
Herald added a subscriber: imp. · View Herald TranscriptSep 6 2018, 5:05 PM
Harbormaster completed remote builds in B19437: Diff 47757.Sep 6 2018, 5:05 PM
kib added inline comments.Sep 6 2018, 5:54 PM
sys/amd64/amd64/support.S
929 ↗(On Diff #47757)

This leaks eflags.ac ?

mjg added inline comments.Sep 6 2018, 6:19 PM
sys/amd64/amd64/support.S
929 ↗(On Diff #47757)

If you mean this gives an exit which leaves smap disabled, then no. There are 2 ways out of stac-ed region: through this label and by falling down to copyinstr_succ. Both have clac. ​copyinstr_toolong_smap was introduced specifically to clac and and then fallback to previously seen ​copyinstr_toolong.

If that's not what you meant, please elaborate.

kib accepted this revision.Sep 6 2018, 6:42 PM
kib added inline comments.
sys/amd64/amd64/support.S
929 ↗(On Diff #47757)

Ah, I missed the _smap.

This revision is now accepted and ready to land.Sep 6 2018, 6:42 PM
Closed by commit rS338508: amd64: depessimize copyinstr_smap (authored by mjg). · Explain WhySep 6 2018, 7:42 PM
This revision was automatically updated to reflect the committed changes.

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sys/
amd64/
amd64/
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Diff 47771

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head/sys/amd64/amd64/support.S

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