docs/76515: missleading use of make -j flag in handbook

[Giorgos Keramidas]

The following reply was made to PR docs/76515; it has been noted by GNATS.

From: Giorgos Keramidas <keramida at freebsd.org>
To: pete wright <pete at nomadlogic.org>
Cc: bug-followup at freebsd.org
Subject: Re: docs/76515: missleading use of make -j flag in handbook
Date: Fri, 21 Jan 2005 14:38:27 +0200

 On 2005-01-20 23:11, pete wright <pete at nomadlogic.org> wrote:
 > http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html
 > states that:
 
 > "It is now possible to specify a -j option to make which will cause
 > it to spawn several simultaneous processes. This is most useful on
 > multi-CPU machines. However, since much of the compiling process is
 > IO bound rather than CPU bound it is also useful on single CPU
 > machines."
 >
 > After testing this out on a SMP system doing a:
 > $ make -jN buildworld
 > (when "N" ranges from 1 to 8) I found that compile times do *not*
 > decrease after starting two make jobs (make -j2 buildworld).
 > This was also tested by others on Uniproc machines and they did not
 > find a decrease in time after starting one make job [...]
 
 There have been problems with running multiple make instances in the
 past.  I'd probably argue for entirely removing the recommendation
 for -j from the Handbook.
 
 New users should never use it, because they don't be able to easily
 troubleshoot broken builds.  Experienced users will probably know if
 it's safe to use -j, by experimenting and reading relevant material in
 the make(1) manpage.
 
 - Giorgos