[Unix-jun72] Why is V1 so slow?

Warren Toomey wkt at tuhs.org
Mon May 5 07:36:32 EDT 2008


On Mon, May 05, 2008 at 07:10:11PM +1000, Peter Jeremy wrote:
> On Mon, May 05, 2008 at 02:52:29PM +1000, Warren Toomey wrote:
> >    i= *c & 0277;
>              ^^^^ 0377 maybe

Yep :)
 
> >But it's very sloooow. I wonder why; V7 on simh is much faster than V1.
> 
> Is V1 executing more instructions to get the same thing done or is simh
> managing to execute V7 instruction streams (or maybe emulate higher-end
> PDP-11's) better?  Judging by some of the earlier hardware comments,
> maybe V1 is thrashing.

I think there are output delays in the kernel, probably to deal with
the speed of mechanical output devices. When I use the compiler, the
compilations are fast, but doing an ls -l /bin takes ages. We might be
able to tweak out the delays.

For example, grep delay build/u9.s, and these lines in u4.s:

1:
       cmp     r1,$11 / char = ht
       bne     1f
       movb    $15.,toutt+0 / set time out to 15 clock tics
1:
       cmp     r1,$15 / char = cr
       bne     2f
       movb    $15.,toutt+0 / set time out to 15 clock ticks
2:
       rts     r0

Cheers,
	Warren



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