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[PATCH] x86/APIC: no need for timer calibration when using TDT
- To: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 17 Jan 2022 11:32:11 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Mon, 17 Jan 2022 10:32:31 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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>
--- 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;
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