Re: Periodic clock tick considered harmful (was: Re: HZ, preferably as

[george anzinger]

Alan Cox wrote:
> 
> > First blush is HELL YES!  The issue is accounting.  When you
> > ask how long a program ran, you are looking at the
> > accounting that happens on a tick.  This is where one of two
> 
> Thats also an implementation issue. Note that the current code is also
> wildly inaccurate. Mr Shannon says we are good to at best 50 run/sleep
> changes a second.  I've got "100% busy" workloads that are 99% asleep.
> 
> Tracking cpu usage at task switch works a lot better for newer processors
> which as well as having rdtsc also have performance counters. In fact you
> can do much more interesting things on modern PC class platforms like
> scheduling using pre-emption interrupts based on instructions executed,
> memory accesses and more.
> 
Oh, I agree.  Hardware could make all this a lot easier.  
-- 
George Anzinger   [e-mail]
High-res-timers: 
http://sourceforge.net/projects/high-res-timers/
Real time sched:  http://sourceforge.net/projects/rtsched/
Preemption patch:
http://www.kernel.org/pub/linux/kernel/people/rml