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    Subject[PATCH 06/27] nohz: Basic full dynticks interface
    Date
    Start with a very simple interface to define full dynticks CPU:
    use a boot time option defined cpumask through the "full_nohz="
    kernel parameter.

    Make sure you keep at least one CPU outside this range to handle
    the timekeeping.

    Also full_nohz= must match rcu_nocb= value.

    Suggested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Alessio Igor Bogani <abogani@kernel.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Chris Metcalf <cmetcalf@tilera.com>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Geoff Levand <geoff@infradead.org>
    Cc: Gilad Ben Yossef <gilad@benyossef.com>
    Cc: Hakan Akkan <hakanakkan@gmail.com>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    ---
    include/linux/tick.h | 7 +++++++
    kernel/time/Kconfig | 9 +++++++++
    kernel/time/tick-sched.c | 23 +++++++++++++++++++++++
    3 files changed, 39 insertions(+), 0 deletions(-)

    diff --git a/include/linux/tick.h b/include/linux/tick.h
    index 553272e..2d4f6f0 100644
    --- a/include/linux/tick.h
    +++ b/include/linux/tick.h
    @@ -157,6 +157,13 @@ static inline u64 get_cpu_idle_time_us(int cpu, u64 *unused) { return -1; }
    static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
    # endif /* !NO_HZ */

    +#ifdef CONFIG_NO_HZ_FULL
    +int tick_nohz_full_cpu(int cpu);
    +#else
    +static inline int tick_nohz_full_cpu(int cpu) { return 0; }
    +#endif
    +
    +
    # ifdef CONFIG_CPU_IDLE_GOV_MENU
    extern void menu_hrtimer_cancel(void);
    # else
    diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
    index 8601f0d..dc6381d 100644
    --- a/kernel/time/Kconfig
    +++ b/kernel/time/Kconfig
    @@ -70,6 +70,15 @@ config NO_HZ
    only trigger on an as-needed basis both when the system is
    busy and when the system is idle.

    +config NO_HZ_FULL
    + bool "Full tickless system"
    + depends on NO_HZ && RCU_USER_QS && VIRT_CPU_ACCOUNTING_GEN && RCU_NOCB_CPU && SMP
    + select CONTEXT_TRACKING_FORCE
    + help
    + Try to be tickless everywhere, not just in idle. (You need
    + to fill up the full_nohz_mask boot parameter).
    +
    +
    config HIGH_RES_TIMERS
    bool "High Resolution Timer Support"
    depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
    diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
    index ad0e6fa..fac9ba4 100644
    --- a/kernel/time/tick-sched.c
    +++ b/kernel/time/tick-sched.c
    @@ -142,6 +142,29 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
    profile_tick(CPU_PROFILING);
    }

    +#ifdef CONFIG_NO_HZ_FULL
    +static cpumask_var_t full_nohz_mask;
    +bool have_full_nohz_mask;
    +
    +int tick_nohz_full_cpu(int cpu)
    +{
    + if (!have_full_nohz_mask)
    + return 0;
    +
    + return cpumask_test_cpu(cpu, full_nohz_mask);
    +}
    +
    +/* Parse the boot-time nohz CPU list from the kernel parameters. */
    +static int __init tick_nohz_full_setup(char *str)
    +{
    + alloc_bootmem_cpumask_var(&full_nohz_mask);
    + have_full_nohz_mask = true;
    + cpulist_parse(str, full_nohz_mask);
    + return 1;
    +}
    +__setup("full_nohz=", tick_nohz_full_setup);
    +#endif
    +
    /*
    * NOHZ - aka dynamic tick functionality
    */
    --
    1.7.5.4


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