From owner-freebsd-hackers Mon Apr 8 15:12:50 1996 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id PAA05656 for hackers-outgoing; Mon, 8 Apr 1996 15:12:50 -0700 (PDT) Received: from phaeton.artisoft.com (phaeton.Artisoft.COM [198.17.250.211]) by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id PAA05650 for ; Mon, 8 Apr 1996 15:12:45 -0700 (PDT) Received: (from terry@localhost) by phaeton.artisoft.com (8.6.11/8.6.9) id PAA03097; Mon, 8 Apr 1996 15:05:10 -0700 From: Terry Lambert Message-Id: <199604082205.PAA03097@phaeton.artisoft.com> Subject: Re: The F_SETOWN problem.. To: bde@zeta.org.au (Bruce Evans) Date: Mon, 8 Apr 1996 15:05:09 -0700 (MST) Cc: louie@TransSys.COM, terry@lambert.org, hackers@FreeBSD.org, jkh@time.cdrom.com, msmith@atrad.adelaide.edu.au, roell@blah.a.isar.de, roell@xinside.com In-Reply-To: <199604081004.UAA25433@godzilla.zeta.org.au> from "Bruce Evans" at Apr 8, 96 08:04:40 pm X-Mailer: ELM [version 2.4 PL24] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-hackers@FreeBSD.org X-Loop: FreeBSD.org Precedence: bulk > >What a SIGIO based scheme does is interrupt whatever computation is > >going on, read the packet from the socket, timestamp it, and put it > >into a queue to be processed at some later time. Once you've noted > >the arrive time, the time criticality is gone, and you can process it > >at your leisure. > > This doesn't help much if there are `M' higher priority hoggish > interrupt handlers that run before the packet's interrupt handler, > and `N' other hog processes in the kernel or in user code that run > before the SIGIO is delivered. Exactly. You can not make Realtime guarantess on a non-Realtime system, and you can't fudge it to pretend you are doing this, and have it work reliably. It's entirely possible that your client command list is going to take a lot of crunching without kernel space calls, and since signals are only handled on call return, you're going to be screwed even with SIGIO. [ ... ] > >Of course, some of us are really weird this way. That how we end up > >with PLL models of the computer's clock in the kernel. > > Some of us wouldn't settle for an offset of 7 digits of nanoseconds :-). 8-). Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.