SMP & CPU_SUSP_HLT

[Bruno Van Den Bossche]

On Sat, 21 Jun 2003 02:47:42 +0100 (BST)
RMH <rmhlldr at yahoo.co.uk> wrote:

> Hello gentlemen,
> 
> it seems CPU_SUSP_HLT does nothing for SMP kernels.
> 
> i386/i386/machdep.c:
> 
> #ifdef SMP
> static int      cpu_idle_hlt = 0;
> #else
> static int      cpu_idle_hlt = 1;
> #endif
> 
> It's noted that when enabled it will result in about 4.2%
> loss in performance while doing buildworld. I haven't
> checked with that, but I tested single-threaded applications
> to suffer for about 2%, what shouldn't be a big difference.
> 
> Beyond power consumption, suspend on HLT may solve some
> overheating issues common for multiprocessor systems. At
> least, it does so in my case.
> 
> I suggest to remove #ifdef SMP, and place a warning into
> NOTES. Let people decide.

People can decide :-)
You can set 'machdep.cpu_idle_hlt: 1' with sysctl.  This will enable the
hlt's for you.  On single cpu-systems this is set by default.  On
SMP-systems it isn't, because of the "loss" in performance you already
mentioned.

-- 
Bruno

Weinberg's Principle: An expert is a person who avoids the small
errors while sweeping on to the grand fallacy.