Date: Thu, 17 Aug 2006 09:41:11 -0500 From: Dan Nelson <dnelson@allantgroup.com> To: Bill LeFebvre <bill@lefebvre.org> Cc: freebsd-stable@freebsd.org Subject: Re: TOP shows above 100% WCPU usage Message-ID: <20060817144110.GB88424@dan.emsphone.com> In-Reply-To: <44E3FE61.6060800@lefebvre.org> References: <44E1F796.5070105@rogers.com> <20060815172728.GB88051@dan.emsphone.com> <44E204C0.60806@rogers.com> <44E3FE61.6060800@lefebvre.org>
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In the last episode (Aug 17), Bill LeFebvre said:
> Mike Jakubik wrote:
> >Dan Nelson wrote:
> >>>How can mysql use 160%? Is this a reporting bug in top because mysql
> >>>is threaded?
> >>You have multiple CPUs, so a threaded process can theoretically reach
> >>100*ncpus cpu usage.
> >
> >Ahh, thats makes sense, thanks.
>
> Actually it doesn't. IMO, %CPU should be biased for all available
> cpu, not just a single cpu. In other words, a single-threaded
> process running on a two processor box should never see more than 50%
> cpu. That's how top computes it for SunOS. But for freebsd top only
> displays whats in the proc structure and I don't know off-hand how
> the kernel records it.
One problem is that method doesn't scale to lots of CPUs. On a Sun
T2000 a non-threaded process consuming all of one CPU would only report
3.12 %CPU in that case (100/32).
I just built top-3.6 on such a system, though, and it does report a
simple "main(){for(;;);}" process as consuming 100 %CPU. Maybe you're
thinking of Solaris's own prstat command?
--
Dan Nelson
dnelson@allantgroup.com
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