From: Jan Beulich <jbeulich@suse.com>
Date: Mon, 24 Jan 2022 07:38:55 +0000 (+0100)
Subject: x86/APIC: no need for timer calibration when using TDT
X-Git-Tag: archive/raspbian/4.17.0-1+rpi1^2~33^2~1122
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=0731a56c7c72;p=xen.git

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@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
---

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;