Date: Thu, 20 Jan 2005 23:11:56 GMT From: pete wright <pete@nomadlogic.org> To: freebsd-gnats-submit@FreeBSD.org Subject: docs/76515: missleading use of make -j flag in handbook Message-ID: <200501202311.j0KNBuTB075049@www.freebsd.org> Resent-Message-ID: <200501202320.j0KNK1pr083557@freefall.freebsd.org>
next in thread | raw e-mail | index | archive | help
>Number: 76515 >Category: docs >Synopsis: missleading use of make -j flag in handbook >Confidential: no >Severity: non-critical >Priority: low >Responsible: freebsd-doc >State: open >Quarter: >Keywords: >Date-Required: >Class: doc-bug >Submitter-Id: current-users >Arrival-Date: Thu Jan 20 23:20:01 GMT 2005 >Closed-Date: >Last-Modified: >Originator: pete wright >Release: 5.3-STABLE >Organization: nomadlogic.org >Environment: FreeBSD finn.nomadlogic.org 5.3-STABLE FreeBSD 5.3-STABLE #1: Tue Jan 4 19:06:52 EST 2005 root@finn.nomadlogic.org:/usr/obj/usr/src/sys/SMP i386 >Description: At: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html It 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 (make -j1 buildworld). Here are edited results on my SMP system: building world with 1 jobs... real 95m20.543s user 83m18.550s sys 13m20.120s cleaning /usr/src.... building world with 2 jobs... real 54m15.856s user 84m42.337s sys 16m39.216s cleaning /usr/src.... building world with 3 jobs... real 53m53.239s user 85m12.189s sys 17m13.039s cleaning /usr/src.... building world with 4 jobs... real 53m56.539s user 85m22.767s sys 17m22.433s >How-To-Repeat: Here is the script I used to produce these results: #!/usr/local/bin/bash MAX=8 for ((i=1; i <= MAX ; i++)) do echo "cleaning /usr/src...." sudo make clean > /home/pete/tmp/clean echo "building world with $i jobs..." time make -j$i buildworld > /home/pete/tmp/build_world_$i echo "" sleep 90 done >Fix: It seems that the -j flag is usefull only in direct proportion to the amount of CPU's available to the system. Maybe the doc should be corrected to relate this. >Release-Note: >Audit-Trail: >Unformatted:
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200501202311.j0KNBuTB075049>