linux-kernel - [PATCH 4.14 62/68] x86/xen/time: set pvclock flags on xen_time

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Message-Id: <20190129113137.576594862@linuxfoundation.org>
Date:   Tue, 29 Jan 2019 12:36:24 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Joao Martins <joao.m.martins@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>
Subject: [PATCH 4.14 62/68] x86/xen/time: set pvclock flags on xen_time_init()

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Joao Martins <joao.m.martins@...cle.com>

commit b888808093113ae7d63d213272d01fea4b8329ed upstream.

Specifically check for PVCLOCK_TSC_STABLE_BIT and if this bit is set,
then set it too on pvclock flags. This allows Xen clocksource to use it
and thus speeding up xen_clocksource_read() callers (i.e. sched_clock())

Signed-off-by: Joao Martins <joao.m.martins@...cle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Signed-off-by: Juergen Gross <jgross@...e.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/xen/time.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -373,6 +373,7 @@ static const struct pv_time_ops xen_time
 
 static void __init xen_time_init(void)
 {
+	struct pvclock_vcpu_time_info *pvti;
 	int cpu = smp_processor_id();
 	struct timespec tp;
 
@@ -396,6 +397,14 @@ static void __init xen_time_init(void)
 
 	setup_force_cpu_cap(X86_FEATURE_TSC);
 
+	/*
+	 * We check ahead on the primary time info if this
+	 * bit is supported hence speeding up Xen clocksource.
+	 */
+	pvti = &__this_cpu_read(xen_vcpu)->time;
+	if (pvti->flags & PVCLOCK_TSC_STABLE_BIT)
+		pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
+
 	xen_setup_runstate_info(cpu);
 	xen_setup_timer(cpu);
 	xen_setup_cpu_clockevents();