Date: Fri, 21 Jan 2005 12:40:32 GMT From: Giorgos Keramidas <keramida@freebsd.org> To: freebsd-doc@FreeBSD.org Subject: Re: docs/76515: missleading use of make -j flag in handbook Message-ID: <200501211240.j0LCeWf3010345@freefall.freebsd.org>
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The following reply was made to PR docs/76515; it has been noted by GNATS. From: Giorgos Keramidas <keramida@freebsd.org> To: pete wright <pete@nomadlogic.org> Cc: bug-followup@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@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
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