Re: announce: PPSkit patch for Linux 2.4.2 (pre6)

["H. Peter Anvin" <hpa@zytor.com>]

Followup to:  <3AD2CE98.28151.46E93A@localhost>
By author:    "Ulrich Windl" <Ulrich.Windl@rz.uni-regensburg.de>
In newsgroup: linux.dev.kernel
>
> Hi,  Cycle Counters,
> 
> Linux currently tries to synchronize TSCs for consistent time in SMP 
> systems. One would not believe what combinations of hardware are tried, 
> especially for precision timing. Here's a short answer to my asking-
> back about a complaint (the kernel is reporting negative time warps).
> 
> As any problem, it can be solved with some overhead, but should it be 
> done?
> 
> Replies to me too, as I'm not subscribed, please.
> 
> > 
> > I have to tell you that I have one 533 MHz Celeron and one 433 MHz
> > Celeron.
> > 

Hi there,

We have talked about assymmetric multiprocessor configurations once or
twice around.  The easy way to deal with them is simply to use
"no-tsc" on the command line (and/or compile your kernel
appropriately.)  One could, at least theoretically, make them usable
in kernel space only (in user space there is no hope, since you can't
know which CPU's TSC you're reading), but these machines seem to be so
rare that hardly anyone technical enough to fix it cares.

	-hpa
-- 
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