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Netbooted bands run slower?

    Date: Tue, 15 May 90 00:46:53 EDT
    From: barmar@Think.COM

    One of my users mentioned to me that he never uses netboot because he
    noticed that they run slower than locally-booted bands.  He says that he's
    noticed a 10% slowdown from running a netbooted band compared to the
    identical band loaded from a local disk.  Has anyone else noticed this?
    I'm at a loss to explain why this should be.  The best guess I have is that
    the world load files tend to have better disk locality than the paging
    files, so when the band is copied into the paging files there's more disk
    arm motion required.  But I'm not sure why paging files should be
    significantly more fragmented on the disk than world load files.  Most of
    our disks were originally formatted at least 2.5 years ago, and have gone
    through several Genera releases, so the FEP file systems are likely to be
    reasonably fragmented.


If anything, I have usually noticed 1better0 performance on netbooted
bands, which I chalked up to the netboot process removing any
"discontiguity" that results from IDS's.  When netboot allocates pages
from swap for the world it tries to allocate the world pages for each
region contiguously, if possible, with (some) room at the end of each
region for growth (also contiguous).  Clearly it can only do this if
there is a suitable contiguous region available in swap.  Also in a
netbooted band, you have no load-to-swap-migration (it's already
occurred) so you have removed that overhead from write-faults.  

Your theory about fragmented paging files is certainly plausible.  There
is no equivalent of "Norton Utilities" for the LispM (there probably
should be), but the way I try to eliminate fragmentation of world/paging
files is to delete as much as I can from the disk all at once and
recreate them from scratch (easy if you have a two-disk system).  It may
be that simply because that's often the course of action before copying
a new world (delete lots to make room for the new world), world files
end up being less fragmented.  Conversely, if you have a paging file
that you created out of every last block of free space, you can imagine
it will be fragmented.

[You probably know that...]

You can use SI:PRINT-FEP-FILESYSTEM to see how fragmented things are.