linux-kernel - [tip: x86/timers] x86/xen/time: Set the X86_FEATURE_TSC_KNOWN_FREQ flag in xen_tsc

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Message-ID: <159568521657.4006.636725222719551278.tip-bot2@tip-bot2>
Date:   Sat, 25 Jul 2020 13:53:36 -0000
From:   "tip-bot2 for Hayato Ohhashi" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Hayato Ohhashi <o8@....dev>, Ingo Molnar <mingo@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: x86/timers] x86/xen/time: Set the X86_FEATURE_TSC_KNOWN_FREQ
 flag in xen_tsc_khz()

The following commit has been merged into the x86/timers branch of tip:

Commit-ID:     898ec52d2ba05915aaedcdb21bff2e944c883cb8
Gitweb:        https://git.kernel.org/tip/898ec52d2ba05915aaedcdb21bff2e944c883cb8
Author:        Hayato Ohhashi <o8@....dev>
AuthorDate:    Tue, 21 Jul 2020 16:12:31 
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Sat, 25 Jul 2020 15:49:41 +02:00

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>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Link: https://lore.kernel.org/r/20200721161231.6019-1-o8@vmm.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 c8897aa..91f5b33 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);
 }