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[PATCH 1/2] xen/x86: don't send IPI to sync TSC when it is reliable
- To: <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Stefano Stabellini <stefano.stabellini@xxxxxxx>
- Date: Mon, 7 Jul 2025 17:07:11 -0700
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- Cc: <jbeulich@xxxxxxxx>, <andrew.cooper3@xxxxxxxxxx>, <roger.pau@xxxxxxxxxx>, <stefano.stabellini@xxxxxxx>, <Xenia.Ragiadakou@xxxxxxx>, <alejandro.garciavallejo@xxxxxxx>, <Jason.Andryuk@xxxxxxx>
- Delivery-date: Tue, 08 Jul 2025 00:07:38 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On real time configuration with the null scheduler, we shouldn't
interrupt the guest execution unless strictly necessary: the guest could
be a real time guest (e.g. FreeRTOS) and interrupting its execution
could lead to a missed deadline.
The principal source of interruptions is IPIs. Remove the unnecessary
IPI on all physical CPUs to sync the TSC when the TSC is known to be
reliable.
Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>
---
xen/arch/x86/time.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index 59129f419d..bfd022174a 100644
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -2303,6 +2303,10 @@ static void cf_check time_calibration(void *unused)
local_irq_enable();
}
+ if ( boot_cpu_has(X86_FEATURE_CONSTANT_TSC) &&
+ boot_cpu_has(X86_FEATURE_TSC_RELIABLE) )
+ return;
+
cpumask_copy(&r.cpu_calibration_map, &cpu_online_map);
/* @wait=1 because we must wait for all cpus before freeing @r. */
--
2.25.1
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