Re: [PATCH v2] x86: Reduce clock calibration time during slave cpu startup

Ingo Molnar
2011-08-05T10:47:39Z

* Jack Steiner <steiner@sgi.com> wrote:

> +/*
> + * Check if another cpu is in the same socket and has already been calibrated.
> + * If found, use the previous value. This assumes all cores in the same physical
> + * socket have the same core frequency.
> +
> +unsigned long __cpuinit calibrate_delay_is_known(void)
> +{
> + int i, cpu = smp_processor_id();
> +
> + if (!tsc_disabled && !cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC))
> + return 0;
> +
> + for_each_online_cpu(i)
> + if (cpu_data(i).phys_proc_id == cpu_data(cpu).phys_proc_id)
> + return cpu_data(i).loops_per_jiffy;

Hm, why do we have to make such an assumption? Cannot we query the
core frequency?

Thanks,

Ingo