x86: Defer LAPIC calibration until after timecounters are available

[markj]

Summary

This ensures that we have a good reference timecounter for performing
calibration.

Change lapic_setup to avoid configuring the timer when booting, and move
calibration and initial configuration to a new lapic routine,
lapic_calibrate_timer. This calibration will be initiated from
cpu_initclocks(), before an eventtimer is selected.

[jhb]

Is Colin going to work on refining the actual calibration to not always take a full second? At the very least the calibration should probably be using sbinuptime() as the TSC calibration does instead of assuming the DELAY() waits exactly for a second. Seems sensible to refine the calibration in a separate commit though.

[cperciva]

Yes, I asked Mark to get this into the tree first so I could handle the TSC and LAPIC calibration at the same time.

[markj]

In D33206#750402, @jhb wrote:

At the very least the calibration should probably be using sbinuptime() as the TSC calibration does instead of assuming the DELAY() waits exactly for a second.

Note that the next patch removes the use of sbinuptime(), since at SI_SUB_CLOCKS/SI_ORDER_FIRST we don't have usable timehands.

[cperciva]

sys/x86/x86/local_apic.c

357

Not sure why this line is being deleted?

[markj]

Restore a lost comment.

[kib]

sys/x86/x86/local_apic.c

1008

I still want to see the herald line when we use deadline mode, in bootverbose dmesg.

1018–1019

Unless I misread the change, this function (and corresponding switch) is now only executed for BSP, while before it was performed for each CPU. This is perhaps fine, because lapic_et_start() would do whatever is needed to ignite the timecounter.

But then, do we need lapic_setup_timer() at all?

[markj]

• Don't bother with timer setup during boot.
• Restore a bootverbose message.

[markj]

sys/x86/x86/local_apic.c

1018–1019

Hmm, I think calibrate_timer() does not need to call lapic_setup_timer() at all, indeed. Note that without the change, the body of lapic_setup_timer() is not executed at all during boot, as the timer mode is not yet initialized. (It was implicitly set to LAT_MODE_UNDEF before, and this change makes the initialization explicit.) The mode is UNDEF until the timer is started, and that will happen after calibration. So I can remove lapic_setup_timer() and restore the inline implementation in native_lapic_setup().

[kib]

sys/x86/x86/local_apic.c

925

I suggest to move intr_restore() right after lapic_calibrate_initcount().

[markj]

Move a verbose printf out of an interrupts-disabled section.