From owner-freebsd-current Fri Aug 23 23:45:27 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 ABF7637B400 for ; Fri, 23 Aug 2002 23:45:25 -0700 (PDT) Received: from critter.freebsd.dk (critter.freebsd.dk [212.242.86.163]) by mx1.FreeBSD.org (Postfix) with ESMTP id DBC2143E3B for ; Fri, 23 Aug 2002 23:45:24 -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 g7O6fxoc037275; Sat, 24 Aug 2002 08:42:00 +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 15:11:27 PDT." <20020823151127.A82640@iguana.icir.org> Date: Sat, 24 Aug 2002 08:41:59 +0200 Message-ID: <37274.1030171319@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 <20020823151127.A82640@iguana.icir.org>, Luigi Rizzo writes: >ok, i'll look into the ACPI counter. >But you still did not tell me why trying to determine the TSC >skew cannot be done reliably ... > >On Fri, Aug 23, 2002 at 11:44:08PM +0200, Poul-Henning Kamp wrote: >> 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 >... >> 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. > >this one does not give timing info at all, and it is probably >also on the "terribly intrusive" side of the spectrum... Neither does TSC, it tells you how many cpu clock cycles were consumed, but now how (ie: instruction executions, pipeline stalls, cache stalls etc etc). -- 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