[Xen-devel] [PATCH] LAPIC timer accounting fix

[Ben Guthro <bguthro@xxxxxxxxxxxxxxx>]

Offset emulated local APIC timer so it doesn't tick during guest's
timer related processing. Otherwise, guests using the local APIC for
process accounting can see long sequences of process ticks incorrectly
charged to interrupt processing.

Signed-off-by: Ben Guthro <bguthro@xxxxxxxxxxxxxx>
Signed-off-by: Gary Grebus <ggrebus@xxxxxxxxxxxxxxx>

diff -r 68521d709355 xen/arch/x86/hvm/vlapic.c
--- a/xen/arch/x86/hvm/vlapic.c Tue Sep 11 15:33:54 2007 -0400
+++ b/xen/arch/x86/hvm/vlapic.c Tue Sep 11 15:33:54 2007 -0400
@@ -962,6 +962,11 @@ void vlapic_destroy(struct vcpu *v)
     free_domheap_page(vlapic->regs_page);
 }
 
+int is_lvtt_vector(struct vcpu *v, int vector)
+{
+    return (vector == vlapic_lvt_vector(vcpu_vlapic(v), APIC_LVTT));
+}
+
 int is_lvtt(struct vcpu *v, int vector)
 {
     return vcpu_vlapic(v)->pt.enabled &&
diff -r 68521d709355 xen/arch/x86/hvm/vpt.c
--- a/xen/arch/x86/hvm/vpt.c    Tue Sep 11 15:33:54 2007 -0400
+++ b/xen/arch/x86/hvm/vpt.c    Tue Sep 11 15:33:54 2007 -0400
@@ -277,6 +277,13 @@ void create_periodic_time(
     pt->period_cycles = (u64)period * cpu_khz / 1000000L;
     pt->one_shot = one_shot;
     pt->scheduled = NOW() + period;
+    if (is_lvtt_vector(v, irq))
+    {
+        /* Try to offset local APIC ticks from timer ticks.  Otherwise, guests
+           using the local APIC for process accounting can see long sequences
+           of process ticks incorrectly charged to interrupt processing. */
+        pt->scheduled += (period >> 1);
+    }
     pt->cb = cb;
     pt->priv = data;
 
diff -r 68521d709355 xen/include/asm-x86/hvm/vlapic.h
--- a/xen/include/asm-x86/hvm/vlapic.h  Tue Sep 11 15:33:54 2007 -0400
+++ b/xen/include/asm-x86/hvm/vlapic.h  Tue Sep 11 15:33:54 2007 -0400
@@ -92,6 +92,7 @@ struct vlapic *apic_round_robin(
 
 int vlapic_match_logical_addr(struct vlapic *vlapic, uint8_t mda);
 
+int is_lvtt_vector(struct vcpu *v, int vector);
 int is_lvtt(struct vcpu *v, int vector);
 int is_lvtt_enabled(struct vcpu *v);
 

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