Date: Tue, 13 Jun 2006 19:36:21 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: Danial Thom <danial_thom@yahoo.com> Cc: freebsd-performance@freebsd.org, David Xu <davidxu@freebsd.org> Subject: Re: Initial 6.1 questions Message-ID: <20060613193040.O26068@fledge.watson.org> In-Reply-To: <20060613182328.76244.qmail@web33304.mail.mud.yahoo.com> References: <20060613182328.76244.qmail@web33304.mail.mud.yahoo.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Tue, 13 Jun 2006, Danial Thom wrote:
> Maybe someone can explain this output. The top line shows 99.6%idle. Is it
> just showing CPU 0s stats on the top line?
Two types of measurements are taken: sampled ticks regarding whether the
system as a while is in {user, nice, system, intr, idle}, and then sampling
for individual processes. Right now, the system measurements are kept in a
simple array of tick counters called cp_time. John Baldwin and others have
changes that make these tick counters per-CPU. The lines at the top of
top(1)'s output are derived from those tick counters. Ticks are measured on
each CPU, so those are a summary across all CPUs. To add cpustat support, we
need to merge John's patch to make cp_time per-CPU (ie., different counters
for different CPUs) and teach the userland tools to retrieve them. When you
run top you'll notice that it adjusts the measurements each refresh. In
effect, what it's doing is sampling the change in tick counts over the window,
pulling down the new values and calculating the percentages of ticks in each
"bucket" in the last window.
Robert N M Watson
Computer Laboratory
Universty of Cambridge
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20060613193040.O26068>