* [PATCH] x86/APIC: no need for timer calibration when using TDT
@ 2022-01-17 10:32 Jan Beulich
2022-01-20 16:09 ` Andrew Cooper
0 siblings, 1 reply; 2+ messages in thread
From: Jan Beulich @ 2022-01-17 10:32 UTC (permalink / raw)
To: xen-devel; +Cc: Andrew Cooper, Wei Liu, Roger Pau Monné
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>
--- 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;
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] x86/APIC: no need for timer calibration when using TDT
2022-01-17 10:32 [PATCH] x86/APIC: no need for timer calibration when using TDT Jan Beulich
@ 2022-01-20 16:09 ` Andrew Cooper
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Cooper @ 2022-01-20 16:09 UTC (permalink / raw)
To: Jan Beulich, xen-devel; +Cc: Andrew Cooper, Wei Liu, Roger Pau Monné
On 17/01/2022 10:32, Jan Beulich wrote:
> 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>
^ permalink raw reply [flat|nested] 2+ messages in thread
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2022-01-17 10:32 [PATCH] x86/APIC: no need for timer calibration when using TDT Jan Beulich
2022-01-20 16:09 ` Andrew Cooper
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