From owner-freebsd-current Fri Aug 23 14:47:34 2002 Delivered-To: freebsd-current@freebsd.org Received: from mx1.FreeBSD.org (mx1.FreeBSD.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 1EE0437B400 for ; Fri, 23 Aug 2002 14:47:33 -0700 (PDT) Received: from critter.freebsd.dk (critter.freebsd.dk [212.242.86.163]) by mx1.FreeBSD.org (Postfix) with ESMTP id 5092443E75 for ; Fri, 23 Aug 2002 14:47:32 -0700 (PDT) (envelope-from phk@critter.freebsd.dk) Received: from critter.freebsd.dk (localhost [127.0.0.1]) by critter.freebsd.dk (8.12.3/8.12.2) with ESMTP id g7NLi8oc030688; Fri, 23 Aug 2002 23:44:08 +0200 (CEST) (envelope-from phk@critter.freebsd.dk) To: Luigi Rizzo Cc: current@FreeBSD.ORG Subject: Re: how to compute the skew between TSC in SMP systems ? In-Reply-To: Your message of "Fri, 23 Aug 2002 14:42:56 PDT." <20020823144256.A82380@iguana.icir.org> Date: Fri, 23 Aug 2002 23:44:08 +0200 Message-ID: <30687.1030139048@critter.freebsd.dk> From: Poul-Henning Kamp Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG In message <20020823144256.A82380@iguana.icir.org>, Luigi Rizzo writes: >I want to find performance problems in the kernel, and to this purpose, >sometimes i need to timestamp events in the kernel using the >least-intrusive technique i can use, and hopefully get reasonably >accurate estimates. If you have a motherboard with ACPI I would use the ACPI counter which runs at 3.mumble MHz, that gives you guaranteed synchronization between CPUs and <300ns resolution. Alternatively, consider using "basic-block profiling" (see kernbb(8) and gcc docs), that will tell you not only how many instructions but also _which_ instructions are executed. -- 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-current" in the body of the message