Path: utzoo!attcan!uunet!lts!amanda
From: amanda@lts.UUCP (Amanda Walker)
Newsgroups: comp.protocols.appletalk
Subject: ICMP reaction time (Was: PacerLink weirdness)
Message-ID: <748@lts.UUCP>
Date: 24 Dec 88 08:39:48 GMT
References: <132@sickkids.UUCP> <8812232126.AA24977@merlin.cs.purdue.edu>
Reply-To: amanda@lts.UUCP (Amanda Walker)
Organization: InterCon Systems Corporation, Reston, VA
Lines: 25

sbm@PURDUE.EDU writes:
         NCSA telnet, apparently, either checks for events very often
    (perhaps once every 30ms, judging from the variation of the round-trip
    times), or uses its own socket listener to respond immediately,
    interrupt-style, when packets arrive.

A little of both.  It does indeed use its own socket listener, but the
listener just puts the packet into a queue to be picked up the next
time through the event loop.  Now, since it's an application and
therefore gets most of the machine's cycles, it's spinning through that
event loop awfully fast.  As I understand the description of PacerLink,
it's in a driver instead of an application, and may only be asking to get
tickled every 30 ticks.  This is quick enough for most things, and
doesn't bog down the rest of the system.  Run NCSA under MultiFinder
with "timeslice=30" in your config.tel, and you'll probably see similar
performance on pings.

Note: I've never seen PacerLink; this is just my interpretation of the
figures that were posted.

-- 
Amanda Walker			...!uunet!lts!amanda / lts!amanda@uunet.uu.net
			  InterCon, 11732 Bowman Green Drive, Reston, VA 22090
--							 Phone: (703) 435-8170
C combines the flexibility of assembler with the power of assembler.