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@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@Mopoke:~>
[summer@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@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@bilby ~]$ cat bin/bm.perl
#!/usr/bin/perl
use integer;
$i = 0;
while ($i < 10000)
{
$j = 0;
while ($j < 10000)
{
++$j;
}
++$i;
}
[summer@bilby ~]$
--
Cheers
John
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