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Differential D20160

Reduce umtx-related work on exec and exit
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Authored by mjg on May 4 2019, 10:38 PM.
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kib
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rS347355: Reduce umtx-related work on exec and exit
Summary

Vast majority of the time there is no need to do anything. The patch below avoids relocking proc and locking umtx + thread lock in the common case.

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rS FreeBSD src repository - subversion
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mjg created this revision.May 4 2019, 10:38 PM
Herald added a subscriber: imp. · View Herald TranscriptMay 4 2019, 10:38 PM
Harbormaster completed remote builds in B24109: Diff 57055.May 4 2019, 10:38 PM
kib added inline comments.May 5 2019, 10:06 AM
sys/kern/kern_umtx.c
4422 ↗(On Diff #57055)

So your problem is this PROC_UNLOCK() ?

I think it can be done much simpler. Since the process is single-threaded, its thread list must be stable there and you can avoid acquiring the PROC_LOCK() in umtx_exec_hook at all.

Of course the proper comment is due.

mjg updated this revision to Diff 57143.May 7 2019, 7:56 PM
  • remove proc locking in the first place
Harbormaster completed remote builds in B24138: Diff 57143.May 7 2019, 7:56 PM
mjg added inline comments.May 7 2019, 7:57 PM
sys/kern/kern_umtx.c
4422 ↗(On Diff #57055)

I'm after avoidable locks in general. umtx shows up as a minor global lock in the grand scheme of things, I don't see what's the problem plugging it.

kib accepted this revision.May 8 2019, 8:16 AM
kib added inline comments.
sys/kern/sched_ule.c
1871 ↗(On Diff #57143)

Why not write this part as

  if (td->td_lend_user_pri == prio ||
   td->td_user_pri == min(prio, td->td_base_user_pri) ||
   td->td_priority < td->td_user_pri)
	return;
  thread_lock(td);
  ...
This revision is now accepted and ready to land.May 8 2019, 8:16 AM
mjg added inline comments.May 8 2019, 4:27 PM
sys/kern/sched_ule.c
1871 ↗(On Diff #57143)

I wanted to keep this easier to modify should extra code be needed in the future.

Closed by commit rS347355: Reduce umtx-related work on exec and exit (authored by mjg). · Explain WhyMay 8 2019, 4:30 PM
This revision was automatically updated to reflect the committed changes.

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Diff 57187

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head/sys/kern/kern_umtx.c

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head/sys/kern/sched_4bsd.c

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head/sys/kern/sched_ule.c

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head/sys/sys/sched.h

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