Re: [PATCH] tsc-disable_B9

[Pavel Machek]

Hi!

> >> And following your argument that these apps have been silenty broken
> >> since 1999, if there's no broken app out there, nobody will ever get the
> >> instruction fault. If there's any app broken out there we probably like
> > 
> > No. rdtsc is still usefull if you are clever and statistically filter
> > out. Also rdtsc provides you number of cycles, so if you want to know
> > how many cycles mov %eax,%ebx takes, you can do that even on
> > speedstep. Anything that correlates rdtsc to real time is broken, however.
> 
> It's not correlating it to real time that's the problem. It's getting resceduled
> inbetween calls that hurts. Take your example.
> 
> rdtsc
> mov %eax,%ebx
> 			<- get rescheduled here
> rdtsc
> 
> Broken. May even take negative "time".

Yep, you need to do 10000 tries and then choose the most common one.

But I believe andrea was talking about apps that corelate rdtsc to real time.