amd64: lapic_timer_rearm: don't reset mode, mask, divisor

The apic timer mode, mask, and divisor are set during lapic_timer_trigger().
We don't need to reset them when rearming the timer.  On physical hardware
the difference is too small to measure, but skipping two apic writes may be
a bit faster when we're running in a VM.

Bochs also likes to log when the apic divisor is changed:

38569516308i[APIC0 ] set timer divide factor to 1
38569517335i[APIC0 ] set timer divide factor to 1
38569518042i[APIC0 ] set timer divide factor to 1
[...]

With this change, Bochs is a lot less noisy.

Idea from mlarkin@.

ok mlarkin@

diff --git a/sys/arch/amd64/amd64/lapic.c b/sys/arch/amd64/amd64/lapic.c
index 6c8ccdf..a5d6d28 100644 (file)
--- a/sys/arch/amd64/amd64/lapic.c
+++ b/sys/arch/amd64/amd64/lapic.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: lapic.c,v 1.66 2023/01/31 19:11:47 cheloha Exp $      */
+/*     $OpenBSD: lapic.c,v 1.67 2023/03/08 18:05:05 cheloha Exp $      */
 /* $NetBSD: lapic.c,v 1.2 2003/05/08 01:04:35 fvdl Exp $ */
 
 /*-
@@ -431,7 +431,7 @@ lapic_timer_rearm(void *unused, uint64_t nsecs)
        cycles = (nsecs * lapic_timer_nsec_cycle_ratio) >> 32;
        if (cycles == 0)
                cycles = 1;
-       lapic_timer_oneshot(0, cycles);
+       lapic_writereg(LAPIC_ICR_TIMER, cycles);
 }
 
 void