Bug in csh time built-in

[Paul Ashton]

[ Sorry if this problem has already been reported ]

There seems to be a bug in the csh built-in time command.  I noticed it
in the SunOS 4.0 csh, and it is also present in the 4.3BSD csh. 

The problem is that the csh built-in time command assumes that the clock
ticks at 100 ticks per second (or 100Hz).  While this is a perfectly
valid assumption on our Vax 750 (running 4.3 BSD), it is not a valid
assumption on our Sun 3/50s and 3/60s (running SunOS 4.0.1) where the
clock ticks at 50Hz. 

The problem manifests itself in the printing of the memory figures
printed by time in the form X+Yk (where X is average real memory used by
the text segment, and Y is the average real memory used by both stack
and data segments).  These figures are calculated from the ru_ixrss
(text segment memory), ru_idrss (data segment memory), and ru_isrss
(stack segment memory) fields of the rusage structure returned by
getrusage(2).  (Note in SunOS 4.0 ru_ixrss and ru_ixrss are always 0,
with the total physical memory in use stored in ru_idrss.  This is a
consequence of the fact that in SunOS 4.0 proceses can have an arbitrary
number of segments.  Also both shared and private physical
memory is included in the ru_ixdrss total - so that if a process is
using (say) the shared std C library its ru_idrss includes all pages
from the shared std C library currently in memory). 

The ru_i?rss fields are in units of page ticks (every time the clock
ticks it adds the number of pages in use by the current process to the
ru_i?rss fields of the current process).  To get the average memory
usage the ru_i?rss fields should be divided by the number of CPU ticks
recorded. 

The csh time multiplies the CPU time (in seconds) by 100 to convert it to
ticks, then divides the various ru_i?rss fileds by this to work
out the average memory usage.  On our Sun 3/50s and 3/60s the CPU time
should be multiplied by 50 to get the number ticks i.e.

Calculated              Correct

ru_i?rss                ru_i?rss
--------------          -------------
CPU secs * 100          CPU secs * 50


This means that the average memory usage reported by the csh time
on our Sun 3/50s and 3/60s is about half what it should be.

Side note

The time shell variable can take a second value which is a format
string.  The feature isn't documented in the 4.3 BSD csh(1), but is
documented in the SunOS 4.0.1 csh(1).


-- 
Email: paul at cosc.canterbury.ac.nz
NZ Telecom:     Office: +64 3 667 001 x6350
NZ Post:        Dept of computer Science
                University of Canterbury, Christchurch, New Zealand