Differential D26612

Only clear TDP_NERRNO when needed
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Authored by trasz on Sep 30 2020, 7:07 PM.

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rS366336: Only clear TDP_NERRNO when needed, ie when it's previously been set.

Summary

Only clear TDP_NERRNO when needed, ie when it's previously been set.

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rS FreeBSD src repository - subversion

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Event Timeline

trasz created this revision.Sep 30 2020, 7:07 PM

Herald added a subscriber: imp. · View Herald TranscriptSep 30 2020, 7:07 PM

trasz requested review of this revision.Sep 30 2020, 7:07 PM

Harbormaster completed remote builds in B33904: Diff 77695.Sep 30 2020, 7:07 PM

kib accepted this revision.Sep 30 2020, 7:13 PM

This revision is now accepted and ready to land.Sep 30 2020, 7:13 PM

this adds a branch which likely pessimizes the code

In D26612#592862, @mjg wrote:

this adds a branch which likely pessimizes the code

The branch is already there, you had to check td_pflags anyway. Not to mention that previously the branch was statically mispredicted (the common case is for (td_pflags & TDP_NERRNO) to be 0.

Closed by commit rS366336: Only clear TDP_NERRNO when needed, ie when it's previously been set. (authored by trasz). · Explain WhyOct 1 2020, 6:45 PM

This revision was automatically updated to reflect the committed changes.

trasz added a commit: rS366336: Only clear TDP_NERRNO when needed, ie when it's previously been set..

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head/

sys/

kern/

11 lines

Diff 77746

head/sys/kern/subr_syscall.c

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