UNIX semantics do permit full support for asynchronous I/O

[Steve Nuchia]

In article <BZS.90Aug31173255 at world.std.com> bzs at world.std.com (Barry Shein) writes:
>Do there exist any benchmark or other test results which indicate that
>adding asynch i/o to unix actually yields a performance improvement?

There is little question that it can dramatically speed up selected
applications.  Applications, mostly in the backup arena (afio, ddd)
get substancially improved throughput even using really stupid mechanisms.
In afio's case the mechanism is to do a fork for every write, and it
is still a lot faster than running without the feature enabled.

One poster mentioned as fact that the point behind asynch I/O was
to overlap computation and I/O.  At least in the backup arena the
point is to overlap some I/O (tape) with other I/O (disk).  In this
case it should be clear that the overall system throughput is not
damaged by the presence of an application using (well-implemented)
asynch I/O if the remaining job mix is CPU intensive.

Reference: Winter 88 Usenix, "A Faster UNIX Dump Program", Jeff Polk
and Rob Kolstad (both then of CONVEX).
-- 
Steve Nuchia	      South Coast Computing Services      (713) 964-2462
"To learn which questions are unanswerable, and _not_to_answer_them;
this skill is most needful in times of stress and darkness."
		Ursula LeGuin, _The_Left_Hand_of_Darkness_