Date: Mon, 12 Feb 2001 23:41:10 -0800 From: Kent Stewart <kstewart@urx.com> To: Matthew Emmerton <matt@gsicomp.on.ca> Cc: Jordan Hubbard <jkh@winston.osd.bsdi.com>, Danny Braniss <danny@cs.huji.ac.il>, freebsd-hackers@FreeBSD.ORG Subject: Re: soft updates performance Message-ID: <3A88E516.CE92FFB1@urx.com> References: <Pine.BSF.4.21.0102130225370.64351-100000@xena.gsicomp.on.ca>
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Sorry about the other one. I intended to start over. I did but not the way I wanted :(. Matthew Emmerton wrote: > > On Mon, 12 Feb 2001, Jordan Hubbard wrote: > > > > One other point that I would like to understand is why -j4 takes > > > longer on all of my systems. That goes against what everyone claims > > > should happen. > > > > With how many running processors? If you're running -j4 on a > > uniprocessor system, you're only introducing competition for already > > scarce CPU resources, though -j2 can be a speedup since this allows > > one target build to run while another is in an I/O wait. I've only > > seen a speedup with -j4 when using at least 2 CPUs. > > FWIW, I've got an ancient dual-CPU machine (Pentium 133s) with an onboard > Adaptec 7870 hooked to a pair of SCSI-2 drives. > > With any intensive build activity (make buildworld, or a kernel > recompile), -j8 gives me the best results. (I came to this conclusion > after profiling a kernel build using -j2/4/6/8/10/12.) > > The only explanation I can give in my case is that the onboard 7870 is a > PCI device and is the main bottleneck in the system (my motherboard is a > very interesting EISA/PCI combo, mfgd in 1991). > > Although Jordan's quite right in saying that using anything larger than > -j2 on a uniprocessor machine will usually be futile, in the world of SMP > things are much stranger, so it's good to experiment. (-j8 is > about a 50% speedup over -j2). YMMV. You have me interested now. I should have a dual P-III 866 running in a few days and I will find out. It is intended to end up running 2 or more Ultra-160 scsi HD's. That will come after I get some timing done with ATA-100 IDE HD's on separate controllers. I haven't tried running -j2 and as soon as my base case with no "-jn" specified and softupdate finishes, I will try "-j2". Kent > > -- > Matt Emmerton -- Kent Stewart Richland, WA mailto:kbstew99@hotmail.com http://kstewart.urx.com/kstewart/index.html FreeBSD News http://daily.daemonnews.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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