Invalid memory stats from vmstat and sysctl vm.vmtotal?
jhell at DataIX.net
Thu Dec 1 18:05:38 UTC 2011
On Thu, Dec 01, 2011 at 10:44:58AM -0000, Steven Hartland wrote:
> ----- Original Message -----
> From: "Jason Hellenthal" <jhell at DataIX.net>
> > This goes along with the thoughts I had about 4 months ago tending to some
> > zfs statistics as well top showing greater than 100% actual CPU usage. This
> > is a big pet peave of mine. Its like saying you ate 134% of a bannanna when
> > in all reallity it is impossible. You can never have more than 100% usage of
> > anything and when seen is a clear notice that some math is considerably
> > incorrect leading to other such miscalculations to be performed. Things like
> > the above already have checks in place that ensure no boundries are being
> > crossed/overflowed or underrun but it surely makes processing results building
> > future products a bitch. One instance is the calculation of threads for example
> > firefox can be seen using upto or more 338% of the CPU. Thats impossible its
> > like saying anyones CPU grew by 400%.
> I could understand a bit of overflow as stats are snapshots which may not
> be instuntanious, but 31GB instead of under 8GB is hardly a rounding issue /
> With respect to top showing greater than 100% by how much are you talking?
> Do your realise that each core = 100%? So if you have a quad core your system
> total will be 400% not 100%?
Yeah I realize that but it still would lead you to believe that if a proccessor has 4 cores on the same die then total for each core could only be 25% usage. And the usage for a proccess only consuming full usage of 1 core is 100%. But you can start firefox on a single uniproccessor and like stated above see large usage percents near 338% or greater which is impossible and leads me to believe were forcing calculation for the entire proccess of threads onto tthread 0. This makes accounting pretty difficult.
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