linux-kernel - [PATCH] x86/xen/time: set the X86_FEATURE_TSC_KNOWN_FREQ flag in xen_tsc

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Message-Id: <20200721161231.6019-1-o8@vmm.dev>
Date:   Tue, 21 Jul 2020 16:12:31 +0000
From:   Hayato Ohhashi <o8@....dev>
To:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        sstabellini@...nel.org, Hayato Ohhashi <o8@....dev>
Subject: [PATCH] x86/xen/time: set the X86_FEATURE_TSC_KNOWN_FREQ flag in xen_tsc_khz()

If the TSC frequency is known from the pvclock page,
the TSC frequency does not need to be recalibrated.
We can avoid recalibration by setting X86_FEATURE_TSC_KNOWN_FREQ.

Signed-off-by: Hayato Ohhashi <o8@....dev>
---
 arch/x86/xen/time.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index c8897aad13cd..91f5b330dcc6 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -39,6 +39,7 @@ static unsigned long xen_tsc_khz(void)
 	struct pvclock_vcpu_time_info *info =
 		&HYPERVISOR_shared_info->vcpu_info[0].time;
 
+	setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
 	return pvclock_tsc_khz(info);
 }
 
-- 
2.23.3