Date: Tue, 13 Jul 1999 20:38:01 +1000 From: Peter Jeremy <jeremyp@gsmx07.alcatel.com.au> To: dillon@apollo.backplane.com, freebsd-current@FreeBSD.ORG Subject: LOCK overheads (was Re: "objtrm" problem probably found) Message-ID: <99Jul13.202011est.40341@border.alcanet.com.au>
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To expand on this morning's table:
i386SX-25 486DX2-50 P-133 PII-266 PIII-450 nproc locks
mode 0 1950.23 161.17 39.65 26.31 9.21 EMPTY
mode 1 3340.59 221.74 71.74 24.45 16.48 1 no tight
mode 2 3237.57 222.96 71.18 25.27 23.65 2 no tight
mode 3 3367.65 626.28 282.31 153.29 93.02 1 yes tight
mode 4 3263.64 627.83 285.58 152.94 160.82 2 yes tight
mode 5 9439.15 2168.12 446.16 60.40 37.64 1 no spread
mode 6 10231.96 2170.48 467.39 60.16 89.28 2 no spread
mode 7 10660.05 3271.40 725.80 153.18 88.32 1 yes spread
mode 8 9990.18 2243.56 755.87 155.18 161.08 2 yes spread
mode 9 5544.82 623.13 131.31 49.96 ? EMPTY
mode 10 7234.97 705.60 174.20 64.81 ? 1 no tight
mode 11 7212.14 707.13 178.72 64.87 ? 2 no tight
mode 12 7355.46 1075.49 304.74 182.75 ? 1 yes tight
mode 13 6956.54 1076.95 327.11 180.21 ? 2 yes tight
mode 14 13603.72 2486.87 582.02 100.10 ? 1 no spread
mode 15 13443.54 1808.75 543.97 101.13 ? 2 no spread
mode 16 13731.94 1587.16 717.31 207.12 ? 1 yes spread
mode 17 13379.62 2547.45 800.31 207.70 ? 2 yes spread
This suggests that adding a lock prefix to anything more recent than
a 386 is fairly expensive. Since the 486 book states `1 clock', but
a real example takes more like 20 clocks, it seems that external
factors outweigh the stated execution timings.
Peter
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