linux-kernel - [PATCH v7 3/5] x86/xen/time: set pvclock flags on xen_time

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Date:   Thu, 19 Oct 2017 14:39:16 +0100
From:   Joao Martins <joao.m.martins@...cle.com>
To:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Cc:     Joao Martins <joao.m.martins@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Andy Lutomirski <luto@...capital.net>
Subject: [PATCH v7 3/5] x86/xen/time: set pvclock flags on xen_time_init()

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>
---
Changes since v5:
 * Add Boris RoB

New in v5
---
 arch/x86/xen/time.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 1ecb05db3632..fc0148d3a70d 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -372,6 +372,7 @@ static const struct pv_time_ops xen_time_ops __initconst = {
 
 static void __init xen_time_init(void)
 {
+	struct pvclock_vcpu_time_info *pvti;
 	int cpu = smp_processor_id();
 	struct timespec tp;
 
@@ -395,6 +396,14 @@ 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();
-- 
2.11.0