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    SubjectRe: Interesting analysis of linux kernel threading by IBM
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    Larry McVoy writes:
    > : Or a machine with a lot of users. (For example, a University unix server)

    You rang?

    > : If it wants to be the most efficient desktop machine, then it doesn't
    > : need it NOW. However, the average number of programs people are
    > : running on their machine are increasing, not decreasing.
    >
    > This is a completely unsubstatiated statement. OK, everyone, do this:
    >
    > $ vmstat
    > load free cach swap pgin pgou dk0 dk1 dk2 dk3 ipkt opkt int ctx usr sys idl
    > 0.00 4.3 96.9 0.4 0 0 0 0 0 0 0 0 104 53 0 3 97

    As a concrete example of what you saying: on one of our two
    interactive general-purpose servers we currently have:
    [~]ermine% uptime
    10:33 up 29 days, 15:54, 227 users, load average: 1.61, 1.84, 1.84
    % lusers
    176 telnetd
    9 rlogind
    8 xterm
    217 tcsh
    5 ftpd
    448 imapd-4.1.FINAL
    11 popper
    0 apache
    528 distinct users
    649 sessions
    % vmstat
    Virtual Memory Statistics: (pagesize = 8192)
    procs memory pages intr cpu
    r w u act free wire fault cow zero react pin pout in sy cs us sy id
    51307 29 97K 1424 28K 2629M 139M 169M 769K 167M 6522 237 6K 946 6 6 88

    and on the other we have

    % uptime
    10:37 up 59 days, 2:08, 286 users, load average: 8.96, 7.34, 7.08
    % lusers
    263 telnetd
    7 rlogind
    7 xterm
    285 tcsh
    3 ftpd
    88 imapd-4.1.FINAL
    16 popper
    0 apache
    253 pine
    354 distinct users
    377 sessions

    They're both old (oh, so old) Alphaservers with 1GB RAM: the first
    has 4 x 250MHz CPUs; the second has 2 x 300MHz CPUs (both running
    Digital UNIX as it happens, as you can see from the low uptimes
    compared to our Linux boxes :-).

    > Those people with the load field higher than 10, please tell us what you are
    > doing.

    The second machine above does actually tend go over a load average of
    10 at peak times (to 20 or 30...) but that's when it's even more
    riduculously overloaded (~500 concurrent users our of a user
    population of 12000). As Larry says, even with many hundreds of people
    hammering on an old machine, the load average stays low when the system
    is behaving. Now it *is* possible to make the load average go sky high
    by running silly or buggy programs but we tend to catch and LART the
    users that run them fairly quickly.

    --Malcolm

    --
    Malcolm Beattie <mbeattie@sable.ox.ac.uk>
    Unix Systems Programmer
    Oxford University Computing Services

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