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Differential D17851

Add a custom implementation of cpu_lock_delay() for x86.
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Authored by jhb on Nov 5 2018, 6:13 PM.
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imp
rpokala

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kib
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rS340170: Add a custom implementation of cpu_lock_delay() for x86.
Summary

Avoid using DELAY() since it can try to use spin locks on CPUs without a
P-state invariant TSC. For cpu_lock_delay(), always use the TSC if it
exists (even if it is not P-state invariant) to delay for a microsecond.
If the TSC does not exist, read from I/O port 0x84 to delay instead.

PR: 228768

Test Plan
  • passed make tinderbox (aside from unrelated breakage in arm.GENERIC-NODEBUG)
  • booted in i386 and amd64 VMs
  • original PR reporter booted combined patch on amd64 machine

Diff Detail

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rS FreeBSD src repository - subversion
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Event Timeline

jhb created this revision.Nov 5 2018, 6:13 PM
Harbormaster completed remote builds in B20642: Diff 50034.Nov 5 2018, 6:13 PM
jhb added a parent revision: D17850: Add a delay_tsc() static function for when DELAY() uses the TSC..Nov 5 2018, 6:14 PM
kib accepted this revision.Nov 5 2018, 9:21 PM
kib added inline comments.
sys/x86/x86/delay.c
125 ↗(On Diff #50034)

And there a comment why tsc_is_invariant check is omitted would be useful IMO.

This revision is now accepted and ready to land.Nov 5 2018, 9:21 PM
jhb updated this revision to Diff 50042.Nov 5 2018, 9:43 PM

Expand comment.

This revision now requires review to proceed.Nov 5 2018, 9:43 PM
Harbormaster completed remote builds in B20646: Diff 50042.Nov 5 2018, 9:43 PM
jhb marked an inline comment as done.Nov 5 2018, 9:44 PM
kib accepted this revision.Nov 5 2018, 9:59 PM
This revision is now accepted and ready to land.Nov 5 2018, 9:59 PM
Closed by commit rS340170: Add a custom implementation of cpu_lock_delay() for x86. (authored by jhb). · Explain WhyNov 5 2018, 10:54 PM
This revision was automatically updated to reflect the committed changes.
Herald added subscribers: rpokala, imp. · View Herald TranscriptNov 5 2018, 10:54 PM

Revision Contents
Changeset List

PathSize
head/
sys/
amd64/
include/
2 lines
i386/
include/
2 lines
x86/
x86/
19 lines

Diff 50046

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head/sys/amd64/include/cpu.h

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head/sys/i386/include/cpu.h

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head/sys/x86/x86/delay.c

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