Differential D54821

powerpc: add a best-effort SMP time base sync for G5's that need it
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Authored by adrian on Thu, Jan 22, 5:27 AM.

Details

Reviewers

jhibbits

Group Reviewers

PowerPC

Summary

There's no timebase freeze platform routine registered on my dual 2.3GHz
G5 PPC970FX Apple PowerMac.

For platforms without an explicit timebase freeze/unfreeze, we'll have to
make do with what we have - which for now is an explicit hand-crafted
spinlock/rendezvous method.

For existing platforms, they'll still continue to clock freeze / rendezvous; albeit with some stronger atomic bits now (from jhibbits@.)
Instead of the fallback being "no timesync", implement a best-effort one which does a similar rendezvous barrier between BSP and APs, but instead of freeze/unfreeze the first instruction after the CPUs all register they're ready is to set the timebase.

This has resulted in many reboots of my Powermac G5 dual-socket device
correctly starting and running in SMP mode.

Diff Detail

Repository

rG FreeBSD src repository

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Unit

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Build Status

Buildable 70052
Build 66935: arc lint + arc unit

Event Timeline

adrian created this revision.Thu, Jan 22, 5:27 AM

Herald added subscribers: jhibbits, imp. · View Herald TranscriptThu, Jan 22, 5:27 AM

adrian requested review of this revision.Thu, Jan 22, 5:27 AM

Harbormaster completed remote builds in B70052: Diff 170226.Thu, Jan 22, 5:27 AM

adrian added a reviewer: jhibbits.Thu, Jan 22, 5:27 AM

adrian added a project: PowerPC.

Herald added subscribers: alfredo, luporl, bdragon. · View Herald TranscriptThu, Jan 22, 5:27 AM

adrian added a reviewer: PowerPC.Thu, Jan 22, 5:28 AM

jhibbits added inline comments.Thu, Jan 22, 2:15 PM

sys/powerpc/powermac/platform_powermac.c
415	Instead of cloning the powerpc_smp_timebase_sync() function into an identical fallback, why not just get rid of the dummy_timebase() check, and let it go as-is? The code looks otherwise identical.

adrian added inline comments.Thu, Jan 22, 3:14 PM

sys/powerpc/powermac/platform_powermac.c
415	They're almost but not quite the same: the freeze version starts timebase sync between CPUs, freezes the timebase clock, sets the timebase on all APs, rendezvous them all, then unpauses the best effort version starts timebase sync between CPUs, rendezvous them all, then sets the timebases on all APs immediately after the rendezvous finishes I didn't want to make the one timebase sync function more complicated in case it broke /other/ platforms in doing so. I'd be much happier to combine them together if I had example SMP G4/G5 hardware to test the various code paths but unfortunately I don't, and the QEMU emulation for the old/new era powermacs doesn't currently implement SMP.

adrian added a child revision: D54855: powerpc: disable the TLBIE lock, it's not needed for POWER8.Sat, Jan 24, 3:09 AM

remove extra mttb()

Harbormaster completed remote builds in B70104: Diff 170321.Sat, Jan 24, 4:00 AM

jhibbits added inline comments.Sat, Jan 24, 8:37 PM

sys/powerpc/powermac/platform_powermac.c
481	Do something about these printfs, I don't think users want to see them every boot. A few options I can think of: Get rid of them bootverbose them KTR them

Revision Contents
Changeset List

Path

Size

sys/

powerpc/

powermac/

platform_powermac.c

97 lines

Diff 170226

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sys/powerpc/powermac/platform_powermac.c

powerpc: add a best-effort SMP time base sync for G5's that need itNeeds ReviewPublicActions