linux-kernel - [tip:x86/timers] x86/tsc: Use TSC as sched clock early

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Date:   Thu, 19 Jul 2018 15:32:18 -0700
From:   tip-bot for Pavel Tatashin <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org, tglx@...utronix.de,
        pasha.tatashin@...cle.com, hpa@...or.com
Subject: [tip:x86/timers] x86/tsc: Use TSC as sched clock early

Commit-ID:  4763f03d3d186ce8a1125844790152d76804ad60
Gitweb:     https://git.kernel.org/tip/4763f03d3d186ce8a1125844790152d76804ad60
Author:     Pavel Tatashin <pasha.tatashin@...cle.com>
AuthorDate: Thu, 19 Jul 2018 16:55:40 -0400
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 20 Jul 2018 00:02:42 +0200

x86/tsc: Use TSC as sched clock early

All prerequesites for enabling TSC as sched clock early in the boot
process are available now:

 - Early attempt of TSC calibration

 - Early availablity of static branch patching

If TSC frequency can be established in the early calibration, enable the
static key which switches sched clock to use TSC.

[ tglx: Massaged changelog ]

Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: steven.sistare@...cle.com
Cc: daniel.m.jordan@...cle.com
Cc: linux@...linux.org.uk
Cc: schwidefsky@...ibm.com
Cc: heiko.carstens@...ibm.com
Cc: john.stultz@...aro.org
Cc: sboyd@...eaurora.org
Cc: hpa@...or.com
Cc: douly.fnst@...fujitsu.com
Cc: peterz@...radead.org
Cc: prarit@...hat.com
Cc: feng.tang@...el.com
Cc: pmladek@...e.com
Cc: gnomes@...rguk.ukuu.org.uk
Cc: linux-s390@...r.kernel.org
Cc: boris.ostrovsky@...cle.com
Cc: jgross@...e.com
Cc: pbonzini@...hat.com
Link: https://lkml.kernel.org/r/20180719205545.16512-22-pasha.tatashin@oracle.com

---
 arch/x86/kernel/tsc.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 7ea0718a4c75..9277ae9b68b3 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1408,6 +1408,7 @@ void __init tsc_early_init(void)
 	/* Sanitize TSC ADJUST before cyc2ns gets initialized */
 	tsc_store_and_check_tsc_adjust(true);
 	cyc2ns_init_boot_cpu();
+	static_branch_enable(&__use_tsc);
 }
 
 void __init tsc_init(void)