From owner-freebsd-hackers Tue Feb 5 11:12:24 2002 Delivered-To: freebsd-hackers@freebsd.org Received: from critter.freebsd.dk (critter.freebsd.dk [212.242.86.163]) by hub.freebsd.org (Postfix) with ESMTP id B413537B436 for ; Tue, 5 Feb 2002 11:12:19 -0800 (PST) Received: from critter.freebsd.dk (localhost [127.0.0.1]) by critter.freebsd.dk (8.11.6/8.11.6) with ESMTP id g15J9BM92035; Tue, 5 Feb 2002 20:09:11 +0100 (CET) (envelope-from phk@critter.freebsd.dk) To: nate@yogotech.com (Nate Williams) Cc: John Polstra , hackers@FreeBSD.ORG Subject: Re: A question about timecounters In-Reply-To: Your message of "Tue, 05 Feb 2002 12:04:45 MST." <15456.11469.659090.290513@caddis.yogotech.com> Date: Tue, 05 Feb 2002 20:09:11 +0100 Message-ID: <92033.1012936151@critter.freebsd.dk> From: Poul-Henning Kamp Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG In message <15456.11469.659090.290513@caddis.yogotech.com>, Nate Williams writes: >How are issues (1) and (3) above different? > >ps. I'm just trying to understand, and am *NOT* trying to start a >flame-war. :) :) :) If the starvation happens to hardclock() or rather tc_windup() the effect will be cummulative and show up in permanent jumps in the output of date for instance. In stable hardclock() is spl-protected so this would be _really_ bad news. If the starvation happens in any of {micro|nano}[up]time() (but not the "get&" variants!) the it will result in a single spurious reading. The premise for avoiding locking in the access functions to timecounters where precisely that we could trust them to not be pre-empted for long enough for the hardware to roll over, if this is not the case we loose because the overflow in the hardware counter means that the timecounter we calculate from is not valid for the delta we get from the hardware. I'm not sure this answers your question, if not it is not bad will, just me not understanding the question :-) -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message