Date: Sat, 23 Nov 1996 17:43:09 -0700 From: Steve Passe <smp@csn.net> To: dg@Root.COM Cc: freebsd-smp@freefall.freebsd.org, Peter Wemm <peter@spinner.dialix.com> Subject: Re: SMP -current merge Message-ID: <199611240043.RAA20563@clem.systemsix.com> In-Reply-To: Your message of "Sat, 23 Nov 1996 15:23:25 PST." <199611232323.PAA02050@root.com>
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Hi, I have tested the times reported by "time make" against a stopwatch, and they are accurate to within 0.5 second. I was surprised to see increasingly better times beyond "-j 2". I guess this is from parallelism on the disk accesses, ie when both CPUs are waiting for disk IO on a particular object build, there is another they can work on if jobs > 2. The point of diminishing returns seems to be around 8 jobs. ------------------------------ Summary of kernel build times: --- 1 CPU active, non SMP kernel: # time make: 446.65s real 337.68s user 22.54s system --- 2 CPUs active, idlequeue search in smp_idleloop(): # time make: 597.45s real 373.91s user 147.68s system --- 2 CPUs active, NO idlequeue search in smp_idleloop(): # time make: 433.87s real 332.11s user 44.69s system # time make -j 2: 326.28s real 400.29s user 67.71s system # time make -j 3: 293.41s real 420.08s user 77.28s system # time make -j 4: 285.10s real 425.32s user 79.71s system # time make -j 5: 277.74s real 428.25s user 78.97s system # time make -j 6: 276.35s real 429.64s user 80.22s system # time make -j 7: 274.97s real 432.54s user 80.01s system # time make -j 8: 274.53s real 431.80s user 81.16s system # time make -j 9: 276.46s real 433.53s user 81.20s system -- Steve Passe | powered by smp@csn.net | FreeBSD -----BEGIN PGP PUBLIC KEY BLOCK----- Version: 2.6.2 mQCNAzHe7tEAAAEEAM274wAEEdP+grIrV6UtBt54FB5ufifFRA5ujzflrvlF8aoE 04it5BsUPFi3jJLfvOQeydbegexspPXL6kUejYt2OeptHuroIVW5+y2M2naTwqtX WVGeBP6s2q/fPPAS+g+sNZCpVBTbuinKa/C4Q6HJ++M9AyzIq5EuvO0a8Rr9AAUR tBlTdGV2ZSBQYXNzZSA8c21wQGNzbi5uZXQ+ =ds99 -----END PGP PUBLIC KEY BLOCK-----
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