linux-kernel - [PATCH 1/2] x86/tsc: Avoid a double call if TSC initializes earlier.

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Date:   Mon, 30 Jul 2018 15:54:20 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     <linux-kernel@...r.kernel.org>, <x86@...nel.org>
CC:     <tglx@...utronix.de>, <mingo@...hat.com>, <hpa@...or.com>,
        Dou Liyang <douly.fnst@...fujitsu.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Pavel Tatashin <pasha.tatashin@...cle.com>
Subject: [PATCH 1/2] x86/tsc: Avoid a double call if TSC initializes earlier.

static_branch_enable(&__use_tsc) may be called twice in common case, that
is redundant. And there are also some common functions both in
tsc_early_init() and tsc_init().

Move them into a separate helper function, only call it once.
Also fix comments:
 -s/authorative/authoritative
 -s/cyc2ns_init/tsc_init

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Pavel Tatashin <pasha.tatashin@...cle.com>
Signed-off-by: Dou Liyang <douly.fnst@...fujitsu.com>
---
 arch/x86/kernel/tsc.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 02e416b87ac1..ba0a6b6e0726 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -182,7 +182,7 @@ static void __init cyc2ns_init_boot_cpu(void)
 }
 
 /*
- * Secondary CPUs do not run through cyc2ns_init(), so set up
+ * Secondary CPUs do not run through tsc_init(), so set up
  * all the scale factors for all CPUs, assuming the same
  * speed as the bootup CPU. (cpufreq notifiers will fix this
  * up if their speed diverges)
@@ -1389,7 +1389,7 @@ static bool __init determine_cpu_tsc_frequencies(bool early)
 	}
 
 	/*
-	 * Trust non-zero tsc_khz as authorative,
+	 * Trust non-zero tsc_khz as authoritative,
 	 * and use it to sanity check cpu_khz,
 	 * which will be off if system timer is off.
 	 */
@@ -1421,6 +1421,14 @@ static unsigned long __init get_loops_per_jiffy(void)
 	return lpj;
 }
 
+static void __init enable_use_tsc(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_early_init(void)
 {
 	if (!boot_cpu_has(X86_FEATURE_TSC))
@@ -1429,10 +1437,7 @@ void __init tsc_early_init(void)
 		return;
 	loops_per_jiffy = get_loops_per_jiffy();
 
-	/* Sanitize TSC ADJUST before cyc2ns gets initialized */
-	tsc_store_and_check_tsc_adjust(true);
-	cyc2ns_init_boot_cpu();
-	static_branch_enable(&__use_tsc);
+	enable_use_tsc();
 }
 
 void __init tsc_init(void)
@@ -1456,13 +1461,10 @@ void __init tsc_init(void)
 			setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER);
 			return;
 		}
-		/* Sanitize TSC ADJUST before cyc2ns gets initialized */
-		tsc_store_and_check_tsc_adjust(true);
-		cyc2ns_init_boot_cpu();
+		enable_use_tsc();
 	}
 
 	cyc2ns_init_secondary_cpus();
-	static_branch_enable(&__use_tsc);
 
 	if (!no_sched_irq_time)
 		enable_sched_clock_irqtime();
-- 
2.14.3