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Re: cvs commit: src/sys/i386/isa rc.c
- To: rgrimes@xxxxxxxxxxxxxxxxxxxx, rgrimes@xxxxxxxxxxxxxxxxxx
- Subject: Re: cvs commit: src/sys/i386/isa rc.c
- From: Bruce Evans <bde@xxxxxxxxxxx>
- Date: Sun, 10 Mar 1996 07:09:03 +1100
- Cc: CVS-committers@xxxxxxxxxxxxxxxxxxxx, cvs-all@xxxxxxxxxxxxxxxxxxxx, cvs-sys@xxxxxxxxxxxxxxxxxxxx
- Sender: owner-commit@xxxxxxxxxxx
>Note that this patch really points to a problem in DELAY(X) for X
>smaller than 20. Right now the DELAY code does an X=-20 and never
>really goes into the DELAY loop.
>It seems that on 133Mhz and faster Pentium systems the assumed overhead
>time of 20uS is no longer valid and something needs to be done to
>correct this. This is especially true when calling short DELAY's in
>a loop since that all ends up running from the internal cache.
>If you spot DELAY being called in an loop some place with values of
>20 or below I suggest that the code be corrected to do what I did here
>or we are going to see more of these types of problems as system
>speeds increase.
Very short delays should only have been used when the precise delay
isn't critical. It isn't practical to guarantee a maximum delay
(slow machines take several usec just to call DELAY(), and interrupts
may extend the delay for several thousand usec). Perhaps DELAY()
should guarantee a minimal delay. This would make all the stupid
timeout loops with DELAY(SMALL) give huge timeouts on slow machines
:-(.
Bruce