[xen master] x86/APIC: no need for timer calibration when using TDT

[patchbot@xxxxxxx]

commit 0731a56c7c72fc117b69982e002954645fc3685b
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Jan 24 08:38:55 2022 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Jan 24 08:38:55 2022 +0100

    x86/APIC: no need for timer calibration when using TDT
    
    The only global effect of calibrate_APIC_clock() is the setting of
    "bus_scale"; the final __setup_APIC_LVTT(0) is (at best) redundant with
    the immediately following setup_APIC_timer() invocation. Yet "bus_scale"
    isn't used when using TDT. Avoid wasting 100ms for calibration in this
    case.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/apic.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/apic.c b/xen/arch/x86/apic.c
index d7d5c15155..5d3e1f3952 100644
--- a/xen/arch/x86/apic.c
+++ b/xen/arch/x86/apic.c
@@ -1292,11 +1292,15 @@ void __init setup_boot_APIC_clock(void)
 
     check_deadline_errata();
 
+    if ( !boot_cpu_has(X86_FEATURE_TSC_DEADLINE) )
+        tdt_enable = false;
+
     local_irq_save(flags);
 
-    calibrate_APIC_clock();
+    if ( !tdt_enable || apic_verbosity )
+        calibrate_APIC_clock();
 
-    if ( tdt_enable && boot_cpu_has(X86_FEATURE_TSC_DEADLINE) )
+    if ( tdt_enable )
     {
         printk(KERN_DEBUG "TSC deadline timer enabled\n");
         tdt_enabled = true;
--
generated by git-patchbot for /home/xen/git/xen.git#master