x86: Use sx lock for intr_table_lock.
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Authored by sepherosa_gmail.com on Sep 5 2016, 7:05 AM.

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howard0su_gmail.com
honzhan_microsoft.com
decui_microsoft.com
jhb
imp

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rS305722: x86: Use sx lock for interrupt sources.

Summary

Certain pic_assign_cpu, e.g. msi_assign_cpu can have quite a long call chain. For msi_assign_cpu, mutex makes complex PCI bridge drivers more tricky, e.g. sleep can not be used, etc; it will be too tricky for upcoming Hyper-V PCI bridge driver for PCI pass-through.
It is not used on any hot code path nor non-sleepable context, so sx should have the same effect as mutex.

Test Plan

Tested-by: Dexuan Cui <decui microsoft com> w/ WIP PCI bridge driver for Hyper-V PCI pass-through.

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sepherosa_gmail.com updated this revision to Diff 20051.Sep 5 2016, 7:05 AM

sepherosa_gmail.com retitled this revision from to x86: Use sx lock for intr_table_lock..

sepherosa_gmail.com updated this object.

sepherosa_gmail.com edited the test plan for this revision. (Show Details)

sepherosa_gmail.com added reviewers: jhb, imp, decui_microsoft.com, howard0su_gmail.com, honzhan_microsoft.com.

If no objection comes, it will be committed early next week.

My worry is that this has a negative impact on suspend/resume. (In general suspend/resume can't sleep).) One option perhaps would be to split the lock into a mutex protecting list of PICs (that is what suspend/resume needs) and the intr_table_lock would only protect interrupt_sources[].

In D7784#162182, @jhb wrote:

My worry is that this has a negative impact on suspend/resume. (In general suspend/resume can't sleep).) One option perhaps would be to split the lock into a mutex protecting list of PICs (that is what suspend/resume needs) and the intr_table_lock would only protect interrupt_sources[].

OK, I will take a look into this.

Split intr_table_lock into two. One for intr sources, which is now sx. One for PIC, which stays mutex. Suggested-by: jhb

jhb accepted this revision.Sep 8 2016, 7:36 PM

jhb edited edge metadata.

This revision is now accepted and ready to land.Sep 8 2016, 7:36 PM

Closed by commit rS305722: x86: Use sx lock for interrupt sources. (authored by sephe). · Explain WhySep 12 2016, 4:58 AM

This revision was automatically updated to reflect the committed changes.

ehem_freebsd_m5p.com mentioned this in D38450: kern/intr: replace mutex with shared-exclusive lock.Feb 21 2023, 12:20 AM

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sys/

x86/

intr_machdep.c

43 lines

Diff 20051

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sys/x86/x86/intr_machdep.c

x86: Use sx lock for intr_table_lock.ClosedPublicActions