Re: Is Parallel Programming Hard, And, If So, What Can You Do About It?

On 5/20/2025 7:38 PM, Lynn Wheeler wrote:

Stephen Fuld <sfuld@alumni.cmu.edu.invalid> writes:

I presume you know that the 3880 controller did not do what today we
call command queuing, so I think you were referring to a potential
queue in the host.  That being the case, the controller doesn't know
if there is a queue or not.  So given that, why not start reading
record 1 on the next track.  If a request comes in, you can abandon
the read to service the request - no harm, no foul.  If there isn't,
and you subsequently get a request for that track, it's a big win.
The only potential loss is if you get a request for the track that was
LRU and got pushed out of the cache.

 over optimizing full track read ahead could lock out other tasks that
had competing requirements for other parts of the disk.

Sure.  That is why I asked if, with all the traces you had collected, you determined whether it was worthwhile to do it.
snipped some stories.
I just want to add that I, for one, enjoy your stories of your time with IBM, and all the internal struggles, both technological and "political" the company went through.
--
  - Stephen Fuld
(e-mail address disguised to prevent spam)