On Mon, Nov 20, 2023 at 11:55:28AM +0100, Valentin Schneider wrote:
> __use_tsc is only ever enabled in __init tsc_enable_sched_clock(), so mark
> it as __ro_after_init.
>
> Signed-off-by: Valentin Schneider <vschneid@xxxxxxxxxx>
> ---
> arch/x86/kernel/tsc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 15f97c0abc9d0..f19b42ea40573 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -44,7 +44,7 @@ EXPORT_SYMBOL(tsc_khz);
> static int __read_mostly tsc_unstable;
> static unsigned int __initdata tsc_early_khz;
>
> -static DEFINE_STATIC_KEY_FALSE(__use_tsc);
> +static DEFINE_STATIC_KEY_FALSE_RO(__use_tsc);
So sure, we can absolutely do that, but do we want to take this one
further perhaps? "notsc" on x86_64 makes no sense what so ever. Lets
drag things into this millennium.
---
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 15f97c0abc9d..4cfcf5946162 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -44,7 +44,9 @@ EXPORT_SYMBOL(tsc_khz);
static int __read_mostly tsc_unstable;
static unsigned int __initdata tsc_early_khz;
+#ifndef CONFIG_X86_64
static DEFINE_STATIC_KEY_FALSE(__use_tsc);
+#endif
int tsc_clocksource_reliable;
@@ -230,24 +232,26 @@ static void __init cyc2ns_init_secondary_cpus(void)
*/
noinstr u64 native_sched_clock(void)
{
- if (static_branch_likely(&__use_tsc)) {
- u64 tsc_now = rdtsc();
+#ifndef CONFIG_X86_64
+ if (!static_branch_unlikely(&__use_tsc)) {
+ /*
+ * Fall back to jiffies if there's no TSC available:
+ * ( But note that we still use it if the TSC is marked
+ * unstable. We do this because unlike Time Of Day,
+ * the scheduler clock tolerates small errors and it's
+ * very important for it to be as fast as the platform
+ * can achieve it. )
+ */
- /* return the value in ns */
- return __cycles_2_ns(tsc_now);
+ /* No locking but a rare wrong value is not a big deal: */
+ return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
}
+#endif
- /*
- * Fall back to jiffies if there's no TSC available:
- * ( But note that we still use it if the TSC is marked
- * unstable. We do this because unlike Time Of Day,
- * the scheduler clock tolerates small errors and it's
- * very important for it to be as fast as the platform
- * can achieve it. )
- */
+ u64 tsc_now = rdtsc();
- /* No locking but a rare wrong value is not a big deal: */
- return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
+ /* return the value in ns */
+ return __cycles_2_ns(tsc_now);
}
/*
@@ -291,7 +295,8 @@ int check_tsc_unstable(void)
}
EXPORT_SYMBOL_GPL(check_tsc_unstable);
-#ifdef CONFIG_X86_TSC
+#ifndef CONFIG_X86_64
+#if defined(CONFIG_X86_TSC
int __init notsc_setup(char *str)
{
mark_tsc_unstable("boot parameter notsc");
@@ -310,6 +315,7 @@ int __init notsc_setup(char *str)
#endif
__setup("notsc", notsc_setup);
+#endif
static int no_sched_irq_time;
static int no_tsc_watchdog;
@@ -1556,7 +1562,9 @@ static void __init tsc_enable_sched_clock(void)
/* Sanitize TSC ADJUST before cyc2ns gets initialized */
tsc_store_and_check_tsc_adjust(true);
cyc2ns_init_boot_cpu();
+#ifndef CONFIG_X86_64
static_branch_enable(&__use_tsc);
+#endif
}
void __init tsc_early_init(void)
