Re: Question: Takes about 2s in sched_clock_init() when kernel boots

[Xie XiuQi <xiexiuqi@huawei.com>]

On 2013/10/31 13:29, Younger Liu wrote:
> Hi,
>   When I analyse boot time on ArmV7, I found that it takes
> about 2s in sched_clock_init(), the log is as follow:
> [    0.000000] before:sched_clock_init.
> [    0.000000] start:sched_clock_init.
> [    2.100505] end  :sched_clock_init.
> [    2.103983] before:calibrate_delay.
> 
>   In my config, CONFIG_HAVE_UNSTABLE_SCHED_CLOCK does not config.
> 
>   Are there any suggestions?

see below:
u64 sched_clock_cpu(int cpu)
{
	struct sched_clock_data *scd;
	u64 clock;

	WARN_ON_ONCE(!irqs_disabled());

	if (sched_clock_stable)
		return sched_clock();

	if (unlikely(!sched_clock_running))
		return 0ull;

	scd = cpu_sdc(cpu);
[...]

Unless sched_clock_running is set, it'll return 0. So, the
printk() time stamp is 0 before sched_clock_init calling.

> 
> 	Younger
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 
>