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From: lasse@daab.UUCP (Lars Hammarstrand)
Newsgroups: net.unix-wizards
Subject: Re: Drive/Device driver performens
Message-ID: <162@daab.UUCP>
Date: Tue, 24-Sep-85 17:22:49 EDT
Article-I.D.: daab.162
Posted: Tue Sep 24 17:22:49 1985
Date-Received: Sat, 28-Sep-85 07:42:32 EDT
References: <160@daab.UUCP> <482@nsc-pdc.UUCP>
Reply-To: lasse@daab.UUCP (Lars Hammarstrand)
Organization: Datorisering AB, Stockholm, Sweden
Lines: 56

In article <482@nsc-pdc.UUCP> djg@nsc-pdc.UUCP (Derek Godfrey) writes:
> First what do you mean by faster? smallest latency or greatest
> transfer rate - both of which can be found by specs. Or as I suspect
> greatest aggregate thougth-put on a running system.
>	To get a fisrt order measuerment of I/O overhead:
>	A) get an empty machine.
>	B) write a cpu intensive program (A counting loop that
>	   terminates).
>	C) find out how long that program runs with no activity.
>	D) run the loop and each of the disc tests together.
>	E) the increases in time of execution now represents cpu cycles
>	   (including DMA) not available to it due to the disc accesses.
> Note you are measuring an approximation for what happens in real life
> and does not model multiple requests at random or synchronised times.

Firts of all, thanks for the tip.
(to Derek Godfrey at NCS Portland Development Center, and all other who
'mailed' me)

I did mean the total system throuput, becuase I know that the STDC board
with DMA (and internal i/o overlapping) must be more effective then the dumb
SMD board with programmed-i/o. Even if the transfer rate from a SMD disk to the
board is much faster (1.2 Mbyte/sec), the transfer rate with a "dbra" intstruc-
tion can't be faster than 432 Kbyte/sec on a 68000 system.

With a "dbra" loop, I mean:

loop:	movb	a5+,a4@
	dbra	d7,loop
	
I think that, if load your main cpu with jobs like programmed io and
things like that, you will get a slower system throuput for each device
you connect and most of the times you are intrested of a higher system
thrughput = more users on the system.  RIGHT??

Have anybody out there, used the system profiler(1M) commands in SysV ?
(prfld, prfstat, prfdc, prfsnap and prfpr.)
Can they help me to measure device driver performens, or just fork/exec
overhead and things like that?

Why do I want to know more about these things?, beacuse I would like
to prove that the bad channel in micros, is one of the things that
makes them run much slower than minis even if the cpu speed sometimes is
faster. (recoginizing this?: Our micro XXXXX is faster than a vax750!!)

I my self, is running on a Cromemco 300 with a UniPlus+ SysVr2 port
and I think it's a pretty fair system, but as usualy it can be better if
I can speed up the channels.

	Lars Hammarstrand.
	Datorisering AB, Stockholm, SWEDEN.

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