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    Subject[PATCH v7 1/6] x86/tsc: remove tsc_disabled flag
    Date
    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@oracle.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
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