Date: Thu, 1 Dec 2011 13:05:22 -0500 From: Jason Hellenthal <jhell@DataIX.net> To: Steven Hartland <killing@multiplay.co.uk> Cc: freebsd-hackers@freebsd.org Subject: Re: Invalid memory stats from vmstat and sysctl vm.vmtotal? Message-ID: <20111201180522.GA67513@DataIX.net> In-Reply-To: <1A338C6C470940B386C307641E350A3E@multiplay.co.uk> References: <547298A3C38F407887E1AAAAC487DF6D@multiplay.co.uk> <20111201065722.GA97051@DataIX.net> <1A338C6C470940B386C307641E350A3E@multiplay.co.uk>
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On Thu, Dec 01, 2011 at 10:44:58AM -0000, Steven Hartland wrote: > ----- Original Message ----- > From: "Jason Hellenthal" <jhell@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 / > overflow. I agree > > 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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