From owner-freebsd-hackers Fri Nov 9 9: 3:16 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from rover.village.org (rover.bsdimp.com [204.144.255.66]) by hub.freebsd.org (Postfix) with ESMTP id 4DCD637B405 for ; Fri, 9 Nov 2001 09:03:13 -0800 (PST) Received: from harmony.village.org (harmony.village.org [10.0.0.6]) by rover.village.org (8.11.3/8.11.3) with ESMTP id fA9H3Ca18851; Fri, 9 Nov 2001 10:03:12 -0700 (MST) (envelope-from imp@harmony.village.org) Received: from harmony.village.org (localhost [127.0.0.1]) by harmony.village.org (8.11.6/8.11.6) with ESMTP id fA9H3B753981; Fri, 9 Nov 2001 10:03:11 -0700 (MST) (envelope-from imp@harmony.village.org) Message-Id: <200111091703.fA9H3B753981@harmony.village.org> To: Poul-Henning Kamp Subject: Re: Measuring interrupt latency Cc: Sansonetti Laurent , freebsd-hackers@freebsd.org In-reply-to: Your message of "Fri, 09 Nov 2001 17:42:58 +0100." <574.1005324178@critter.freebsd.dk> References: <574.1005324178@critter.freebsd.dk> Date: Fri, 09 Nov 2001 10:03:11 -0700 From: Warner Losh 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 <574.1005324178@critter.freebsd.dk> Poul-Henning Kamp 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. Hmmmm. Actually looking at the code, we did use nanotime()... But we do have a few drivers that are using getnanotime() incorrectly... The larger variance was something like a factor of 2 larger than the one that we'd measured on the scopes. I don't have the data online, or I'd be more precise. Warner To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message