On Tue, Jun 09, 2015 at 11:13:40AM +0800, Huang Rui wrote:
> +static void delay_mwaitx(unsigned long __loops)
> +{
> + u32 end, now, delay, addr;
> +
> + delay = __loops;
> + rdtsc_barrier();
> + rdtscl(end);
> + end += delay;
> +
> + while (1) {
> + __monitorx(&addr, 0, 0);
> + mwaitx(delay, true);
> +
> + rdtsc_barrier();
> + rdtscl(now);
> + if (end <= now)
> + break;
> + delay = end - now;
> + }
How about you think instead and do something like:
rdtsc(start);
rdtsc_barrier();
for (;;) {
delay = min(MWAIT_MAX_LOOPS, loops);
__monitorx(&addr, 0, 0);
mwaitx(delay, true);
rdtsc_barrier();
rdtsc(end);
rdtsc_barrier();
loops -= end - start;
if (loops <= 0)
break;
start = end;
}
> +}
> +
> +/*
> * Since we calibrate only once at boot, this
> * function should be set once at boot and not changed
> */
> @@ -118,7 +145,12 @@ int read_current_timer(unsigned long *timer_val)
>
> void __delay(unsigned long loops)
> {
> - delay_fn(loops);
> + if (loops > MWAITX_MAX_LOOPS ||
> + !static_cpu_has_safe(X86_FEATURE_MWAITT) ||
> + boot_option_delay != DELAY_MWAITX)
> + delay_fn(loops);
> + else
> + delay_mwaitx(loops);
> }
Then you can do away with that fallback entirely.
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