why is fprintf(stderr,) slow?

[wsmith at uiucdcsb.CS.UIUC.EDU]

I was doing some performance testing on a program and as part of it
I was doing about 500 fprintf(stderr, "blah...\n");

The program was taking 35 or 40 seconds of system time which was pretty
high.  I then commented out the fprintf's and the program took 17 or 18
system time seconds (it was doing a lot of disk accesses).

Is this well known behavior that fprintf(stderr, ... ) takes a lot of time?
Why does it do so?

Bill Smith
ihnp4!uiucdcs!wsmith
wsmith at b.cs.uiuc.edu