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(2/2) threads: reimplement tid allocation on top of a bitmap
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Authored by mjg on Nov 5 2020, 6:48 AM.
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rS367537: threads: reimplement tid allocation on top of a bitmap
Summary

There are workloads with very bursty tid allocation and since unr tries very hard to have small-sized bitmaps it keeps reallocating memory. Just doing buildkernel gives almost 150k calls to free coming from unr.

This also gets rid of the hack which tried to postpone TID reuse.

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rS FreeBSD src repository - subversion
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mjg created this revision.Nov 5 2020, 6:48 AM
Herald added a subscriber: imp. · View Herald TranscriptNov 5 2020, 6:48 AM
mjg requested review of this revision.Nov 5 2020, 6:48 AM
Harbormaster completed remote builds in B34641: Diff 79199.Nov 5 2020, 6:48 AM
mjg updated this revision to Diff 79203.Nov 5 2020, 6:56 AM
mjg edited the summary of this revision. (Show Details)Nov 5 2020, 2:02 PM
markj added inline comments.Nov 5 2020, 2:32 PM
sys/kern/kern_thread.c
142 ↗(On Diff #79203)

Can't both tid_bitmap and tid_lock be static?

198 ↗(On Diff #79203)

Shouldn't it be trytid = tid + 1?

mjg updated this revision to Diff 79216.Nov 5 2020, 2:38 PM
  • staticize tid_lock and tid_bitmap
  • store tid + 1
mjg marked 2 inline comments as done.Nov 5 2020, 2:39 PM
kib added inline comments.Nov 5 2020, 3:57 PM
sys/kern/kern_thread.c
200 ↗(On Diff #79216)

Isn't this off by one ? NO_PID should not be used.

mjg added inline comments.Nov 5 2020, 4:12 PM
sys/kern/kern_thread.c
200 ↗(On Diff #79216)

NO_PID == 100000 goes to thread0 both before and after the patch.

kib accepted this revision.Nov 5 2020, 5:24 PM
kib added inline comments.
sys/kern/kern_thread.c
200 ↗(On Diff #79216)

Ah ok, it is consumed immediately.

This revision is now accepted and ready to land.Nov 5 2020, 5:24 PM
markj accepted this revision.Nov 6 2020, 1:57 PM
Closed by commit rS367537: threads: reimplement tid allocation on top of a bitmap (authored by mjg). · Explain WhyNov 10 2020, 2:14 AM
This revision was automatically updated to reflect the committed changes.
mjg added a commit: rS367537: threads: reimplement tid allocation on top of a bitmap.

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head/sys/kern/kern_thread.c

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