El vie, 08-09-2006 a las 10:59 +0800, John Summerfield escribió: > Jim Perrin wrote: > >> > >> Awesome... Next server has HT.. So I'll give that a try! > > > > > > Keep in mind that HT is its own special brand of hell, and isn't > > really *true* SMP. The kernel will work fine, and you'll see 2x the > > processors, but at most you'll get about a 3% performance boost, and > > at worst, it'll actually hurt performance. Some motherboards have > > buggy HT implementations and may cause some locking or slowness. > > Sometimes this can be resolved by appending apci=ht to your kernel > > boot line. With HT you also have the possibility of cache thrashing, > > which can/will impact performance. Make sure you know what you're > > getting into. > > > > > > It's not all loss. I have a small benchmark written in Perl to exercise > the CPU a little. > I have here two muts (machines under test), > Mopoke's a Dell Pentium IV 3.00 with HT enabled, running Suse 10.1. > Bilby's a Sempron 2500+, so it's a bit slower. Also, it's running > roughly Nahant, so compiled with older (slower?) gcc and different perl. > > What I'm illustrating here is the difference HT can make: > > > summer at Mopoke:~> time bm.perl&time bm.perl&wait > [1] 3480 > [2] 3481 > > real 0m23.935s > user 0m23.689s > sys 0m0.004s > > real 0m25.906s > user 0m24.746s > sys 0m0.004s > [1]- Done time bm.perl > [2]+ Done time bm.perl > summer at Mopoke:~> > [summer at bilby ~]$ time bm.perl&time bm.perl&wait > [1] 10099 > [2] 10100 > > real 0m49.343s > user 0m24.287s > sys 0m0.011s > > real 0m49.371s > user 0m24.405s > sys 0m0.013s > [1]- Done time bm.perl > [2]+ Done time bm.perl > [summer at bilby ~]$ > > > Note that on mopoke, user for each is about equal to elapsed, about what > one wout expect with dual-core or SMP. > > On Bilby, user for each is about half elapsed, just as one would expect. > > For those who like to play by themselves, here's the code: > > [summer at bilby ~]$ cat bin/bm.perl > #!/usr/bin/perl > use integer; > $i = 0; > while ($i < 10000) > { > $j = 0; > while ($j < 10000) > { > ++$j; > } > ++$i; > } > > [summer at bilby ~]$ > > > > > > > Hi John, Comparing your reference with a Dell Dimension 3100 (P4HT, 3.0GHz, 2ML2, 2GB) but with apci=ht enabled, slightly low compared as your SuSe. I'll re-exec on new 42.0.2 next weeks without apci=ht to see differences Fyi i've been working without it for long time without issues on 34.0.2, just incorpored this flag in last times for security/stability after reading others notes) [root at sparkbox ~]# uname -a Linux sparkbox.stigmatedbrain.net 2.6.9-34.0.2.ELsmp #1 SMP Fri Jul 7 19:52:49 CDT 2006 i686 i686 i386 GNU/Linux [root at sparkbox ~]# free total used free shared buffers cached Mem: 2065384 1708756 356628 0 6924 191476 -/+ buffers/cache: 1510356 555028 Swap: 2031608 657924 1373684 [root at sparkbox ~]# cat /etc/grub.conf | grep 2.6.9-34.0.2.ELsmp title CentOS (2.6.9-34.0.2.ELsmp) kernel /vmlinuz-2.6.9-34.0.2.ELsmp ro root=/dev/VolGroup00/LogVol00 selinux=0 vga=0x031a apci=ht initrd /initrd-2.6.9-34.0.2.ELsmp.img [root at sparkbox ~]# cat /var/log/dmesg | grep "CPU: L2" CPU: L2 cache: 2048K CPU: L2 cache: 2048K [root at sparkbox ~]# cat bin/cpubench.pl #!/usr/bin/perl # Usage on HT/MultiCPU host: # time cpubench.pl&time cpubench.pl&wait use integer; $i = 0; while ($i < 10000) { $j = 0; while ($j < 10000) { ++$j; } ++$i; } [root at sparkbox ~]# cat /etc/issue | grep CentOS CentOS release 4.3 (Final) [root at sparkbox ~]# time cpubench.pl&time cpubench.pl&wait [1] 8003 [2] 8005 real 0m30.166s user 0m16.680s sys 0m0.085s real 0m30.809s user 0m16.606s sys 0m0.066s [1]- Done time cpubench.pl [2]+ Done time cpubench.pl Cheers, Jose. -- ----------------------------------------------------------------- sparkbox.stigmatedbrain.net 2.6.9-34.0.2.ELsmp i686 GNU/Linux 08:40:01 up 14 days, 20:13, 76 users, load average: 1.82, 2.48, 2.27 ----------------------------------------------------------------- With regard to precipitous heights, if you are beforehand with your adversary, you should occupy the raised and sunny spots, and there wait for him to come up. --The Art of War by Sun Tzu Chapter X: Terrain