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    SubjectRe: [PATCH 07/33] nohz: Basic full dynticks interface
    On Tue, Jan 08, 2013 at 03:08:07AM +0100, Frederic Weisbecker wrote:

    [ … ]

    > 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"

    I think you want to say here "Almost-completely tickless system".
    "Almost" because of that one CPU outside of the range :-)

    > + 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 314b9ee..494a2aa 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);

    Don't you want to check retval of cpulist_parse first here before
    assigning have_full_nohz_mask and allocating cpumask var?

    We don't trust userspace, you know.

    > + return 1;
    > +}
    > +__setup("full_nohz=", tick_nohz_full_setup);

    I'd guess this kernel parameter needs to go into
    Documentation/kernel-parameters.txt along with a referral to
    Documentation/cputopology.txt which explains how to specify cpulists for
    n00bs like me :-)

    Thanks.

    --
    Regards/Gruss,
    Boris.

    Sent from a fat crate under my desk. Formatting is fine.
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