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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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