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

[tip-bot for Pavel Tatashin]

Commit-ID:  4763f03d3d186ce8a1125844790152d76804ad60
Gitweb:     https://git.kernel.org/tip/4763f03d3d186ce8a1125844790152d76804ad60
Author:     Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
AuthorDate: Thu, 19 Jul 2018 16:55:40 -0400
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: steven.sistare@xxxxxxxxxx
Cc: daniel.m.jordan@xxxxxxxxxx
Cc: linux@xxxxxxxxxxxxxxx
Cc: schwidefsky@xxxxxxxxxx
Cc: heiko.carstens@xxxxxxxxxx
Cc: john.stultz@xxxxxxxxxx
Cc: sboyd@xxxxxxxxxxxxxx
Cc: hpa@xxxxxxxxx
Cc: douly.fnst@xxxxxxxxxxxxxx
Cc: peterz@xxxxxxxxxxxxx
Cc: prarit@xxxxxxxxxx
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Cc: linux-s390@xxxxxxxxxxxxxxx
Cc: boris.ostrovsky@xxxxxxxxxx
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Cc: pbonzini@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20180719205545.16512-22-pasha.tatashin@xxxxxxxxxx

---
 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)