Date: Fri, 23 Aug 2002 23:44:08 +0200 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Luigi Rizzo <rizzo@icir.org> Cc: current@FreeBSD.ORG Subject: Re: how to compute the skew between TSC in SMP systems ? Message-ID: <30687.1030139048@critter.freebsd.dk> In-Reply-To: Your message of "Fri, 23 Aug 2002 14:42:56 PDT." <20020823144256.A82380@iguana.icir.org>
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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
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