From owner-freebsd-hackers Sun Jan 23 18: 8:43 2000 Delivered-To: freebsd-hackers@freebsd.org Received: from dan.emsphone.com (dan.emsphone.com [199.67.51.101]) by hub.freebsd.org (Postfix) with ESMTP id 743D214E03; Sun, 23 Jan 2000 18:08:40 -0800 (PST) (envelope-from dan@dan.emsphone.com) Received: (from dan@localhost) by dan.emsphone.com (8.9.3/8.9.3) id UAA20228; Sun, 23 Jan 2000 20:08:07 -0600 (CST) (envelope-from dan) Date: Sun, 23 Jan 2000 20:08:07 -0600 From: Dan Nelson To: Mikhail Teterin Cc: Jason Evans , David Schwartz , bde@FreeBSD.ORG, hackers@FreeBSD.ORG Subject: Re: kern/13644 Message-ID: <20000123200807.A19917@dan.emsphone.com> References: <20000123121055.F27689@sturm.canonware.com> <200001240126.UAA44772@rtfm.newton> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 1.0.1i In-Reply-To: <200001240126.UAA44772@rtfm.newton>; from "Mikhail Teterin" on Sun Jan 23 20:26:15 GMT 2000 X-OS: FreeBSD 4.0-CURRENT Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG In the last episode (Jan 23), Mikhail Teterin said: > =FreeBSD is clearly not capable of hard real-time. If I > =remember correctly, neither are any of the operating systems from > =which you quoted man pages. That makes *all* of those man pages > =inaccurate. > > In other words, we found a flow in the most (all?) Unix implementations? > Including FreeBSD. Alright. If you want to call it a flaw, then yes. The kernel always has priority over user processes. If an ethernet packet comes in, a character is received over a serial port, or a disk wants to return a block of data requested by the system, your user process *will* stop and the kernel will processes the interrupt. If that interrupt takes a while, a select() or poll() may very well return later than the timeout specified. Apart from writing your own kernel module, blocking all interrupts, and buzz-looping on a timer variable, there's not much you can do about it under Unix. And I'll not even mention what happens to this when you start swapping. -- Dan Nelson dnelson@emsphone.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message