Re: [PATCH] x86: enable preemption in delay

[Steven Rostedt]

On Sun, 25 May 2008, Pavel Machek wrote:
> > +		if (unlikely(cpu != smp_processor_id())) {
> > +			if (loops <= TSC_MIGRATE_COUNT)
> > +				break;
> > +			cpu = smp_processor_id();
> > +			rdtscl(bclock);
> > +			loops -= TSC_MIGRATE_COUNT;
> > +		} else {
> > +			rdtscl(now);
> > +			if ((now - bclock) >= loops)
> > +				break;
> > +			loops -= (now - bclock);
> > +			bclock = now;
>
> What happens with different cpus running on different frequencies...?
> Cpufreq?

It's not even protected with the old code.

inline void __const_udelay(unsigned long xloops)
{
	__delay(((xloops * HZ *
		cpu_data(raw_smp_processor_id()).loops_per_jiffy) >> 32) + 1);
}

Here it calculates the loops_per_jiffy for the CPU and calls into __delay.
But it can easily be preempted here and the delay could run on another
CPU.

-- Steve

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