From owner-freebsd-hackers Sat Nov 10 2:47:54 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from critter.freebsd.dk (dhcp158.rocks.bsdconeurope.org [195.40.100.158]) by hub.freebsd.org (Postfix) with ESMTP id A4C7837B42C for ; Sat, 10 Nov 2001 02:47:51 -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 fA9GgwL00576; Fri, 9 Nov 2001 17:42:58 +0100 (CET) (envelope-from phk@critter.freebsd.dk) To: Warner Losh Cc: Sansonetti Laurent , freebsd-hackers@FreeBSD.ORG Subject: Re: Measuring interrupt latency In-Reply-To: Your message of "Thu, 08 Nov 2001 09:51:36 MST." <200111081651.fA8Gpa744046@harmony.village.org> Date: Fri, 09 Nov 2001 17:42:58 +0100 Message-ID: <574.1005324178@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 <200111081651.fA8Gpa744046@harmony.village.org>, Warner Losh writes: >We found at Timing Solutions when we were trying to measure interrupt >latency that the system time (getnanotime()) gave us measurements with >a larger variance than our expensive scopes that does statistical >gathering. Uhm, you should have used nanotime(), not getnanotime(). getnanotime() returns a timestamp in nanoseconds of the last stored timestamp which may be up to 1/hz seconds old. -- 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