Date: Thu, 14 Sep 2006 19:43:27 +0200 From: Pieter de Goeje <pieter@degoeje.nl> To: Gary Corcoran <gcorcoran@rcn.com> Cc: freebsd-hackers@freebsd.org Subject: Re: numbers don't lie ... Message-ID: <200609141943.28218.pieter@degoeje.nl> In-Reply-To: <45099123.4000500@rcn.com> References: <E1GNOLq-000DC2-1Q@cs1.cs.huji.ac.il> <863bauk3gp.fsf@dwp.des.no> <45099123.4000500@rcn.com>
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On Thursday 14 September 2006 19:28, Gary Corcoran wrote: > The confusing thing is that I thought 'real' time should be >= 'user' + > 'sys'. But here 'user' is much greater than 'real' for both machines! The > sense I got from the other messages in this thread is that 'user' time is > somewhat meaningless (i.e. unreliable as a measure) in a multi-CPU and/or > hyperthreading environment. Can you clarify? user time = time spent in userland on all logical processors combined. The right equation is: real * ncpus > user + sys, where ncpus = number of active logical processors. In the optimal case (perfect parallelism): real * ncpus = user + sys - Pieter
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