NBUF and pstat

[Jim Jagielski]

In article <2859 at redstar.cs.qmw.ac.uk> liam at cs.qmw.ac.uk (William Roberts;) writes:
}In <2657 at dftsrv.gsfc.nasa.gov> jim at jagubox.gsfc.nasa.gov (Jim Jagielski) 
}writes:
}
}
}>Currently, my kernel is built with NBUF being 0, meaning that 10% of
}>the free space at start-up is utilized for disk buffers. I want more.
}>The question is how many buffers are there???
}
}>I would guess, using pstat, that NBUF is actually set to 1551 since
}>that is the value that pstat returns for buffers.... Is this right?
}
}I believe that you are right: 
}

I am :):)

}
}Your figure of 1551 seems very high - let me guess: either you are running a 
}32 Megabyte machine, or you have SBUFSIZE set to 1024 and you are running a 16 
}Meg machine.
}

It's a 32 meg mac with SBUFSIZE 2048... right again!

Anyway, this all leads to an interesting question... certainly, as far as
disk buffers are concerned, there is a point of diminishing returns where
increasing the amount of buffers adds very little or even DECREASES performance
(possibly). Does anyone have any good system tuning information for A/UX...
25% memory for NBUF seems about right, but with large systems (32 megs) that
still leaves a good chunk of free memory... Of course, that isn't bad since
that means that swapping won't occur :)

--
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                                 =:^)
           Jim Jagielski                    NASA/GSFC, Code 711.1
     jim at jagubox.gsfc.nasa.gov               Greenbelt, MD 20771

"Exploding is a perfectly normal medical phenomenon. In many fields of
 medicine nowadays, a dose of dynamite can do a world of good."