linux-kernel - [PATCH v7 1/6] x86/tsc: remove tsc

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Date:   Thu,  2 Nov 2017 13:26:39 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     steven.sistare@...cle.com, daniel.m.jordan@...cle.com,
        linux@...linux.org.uk, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, john.stultz@...aro.org,
        sboyd@...eaurora.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
        douly.fnst@...fujitsu.com
Subject: [PATCH v7 1/6] x86/tsc: remove tsc_disabled flag

tsc_disabled is set when notsc is passed as kernel parameter. The reason we
have notsc is to avoid timing problems on multi-preccors systems. However,
we already have a mechanism to detect and resolve these issues by invoking
tsc unstable path.

Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
---
 arch/x86/kernel/tsc.c | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 796d96bb0821..1c4502a2b7b2 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -37,11 +37,6 @@ EXPORT_SYMBOL(tsc_khz);
  */
 static int __read_mostly tsc_unstable;
 
-/* native_sched_clock() is called before tsc_init(), so
-   we must start with the TSC soft disabled to prevent
-   erroneous rdtsc usage on !boot_cpu_has(X86_FEATURE_TSC) processors */
-static int __read_mostly tsc_disabled = -1;
-
 static DEFINE_STATIC_KEY_FALSE(__use_tsc);
 
 int tsc_clocksource_reliable;
@@ -248,7 +243,7 @@ EXPORT_SYMBOL_GPL(check_tsc_unstable);
 int __init notsc_setup(char *str)
 {
 	pr_warn("Kernel compiled with CONFIG_X86_TSC, cannot disable TSC completely\n");
-	tsc_disabled = 1;
+	mark_tsc_unstable("boot parameter notsc");
 	return 1;
 }
 #else
@@ -1229,7 +1224,7 @@ static void tsc_refine_calibration_work(struct work_struct *work)
 
 static int __init init_tsc_clocksource(void)
 {
-	if (!boot_cpu_has(X86_FEATURE_TSC) || tsc_disabled > 0 || !tsc_khz)
+	if (!boot_cpu_has(X86_FEATURE_TSC) || !tsc_khz)
 		return 0;
 
 	if (tsc_clocksource_reliable)
@@ -1311,12 +1306,6 @@ void __init tsc_init(void)
 		set_cyc2ns_scale(tsc_khz, cpu, cyc);
 	}
 
-	if (tsc_disabled > 0)
-		return;
-
-	/* now allow native_sched_clock() to use rdtsc */
-
-	tsc_disabled = 0;
 	static_branch_enable(&__use_tsc);
 
 	if (!no_sched_irq_time)
@@ -1348,7 +1337,7 @@ unsigned long calibrate_delay_is_known(void)
 	int sibling, cpu = smp_processor_id();
 	struct cpumask *mask = topology_core_cpumask(cpu);
 
-	if (!tsc_disabled && !cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC))
+	if (!cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC))
 		return 0;
 
 	if (!mask)
-- 
2.15.0