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NTVDM speed (or lack thereof) (Announce)

posted by Ninho E-mail, 15.02.2011, 20:27

>> ... For CPU bound apps, NTVDM indeed is awfully slow -
>> independent of display mode.
>
> I've never noticed any slowdown for reasonable apps, but so many things can
> come into play (e.g. cpu, e.g. redir -t befi.com on AMD64x2 Vista was 5x
> slower than without redir). It just depends, but for most normal uses, it's
> the same speed (for me, in my obviously limited experience). By design it's
> not supposed to be much slower at all, so if it is, something went wrong.
Admittedly the pure computing case is rare, and my calculations are extreme - in that they try very hard to run entirely in CPU and mostly in general integer registers; I went to great lengths to avoid hitting memory and even the caches - for instance, when I need to keep a "carry" around a couple instructions, it won't pushf/popf but had rather setc reg8/neg reg8 or even our old pair of friends, lahf/sahf ;=) In such conditions, any context switch is catastrophic, clearly. I wouldn't use Windows or any multitasking OS to run the task seriously, but for tuning my progs and quickly testing the mods of course Windows is convenient and even comfortable.

[More DOS-topical : I never found a good DOS task switcher but for Windows itself. All DOS task switchers that I tried back then... were buggy or deficient or both. IIRC that included taskers from Norton, Central Point (when they had not yet become parts of the same entity), DRDOS's "tasmax", and more. The only half acceptable thing came later, viz the task switcher included by MS with DOS 5 (?) and DOS 6.0 (retired from 6.2 iirc). But of course the latter was a stripped down version or at least derived from the Windows 3.x (real or 'standard' mode) DOSSWAP and was OK. Now I'm not often finding myself praising something from Microshaft...]

Win 2k again : that question about controlling the time quantum - both globally AND per task (process, or thread maybe) is still open, if anyone lurking here has knowledge of hidden parameters (maybe from studying the so-called Research Kernel ?) I'll love to hear from them...

Regards

---
Ninho

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