Author: Robert Hyatt
Date: 19:49:39 04/14/04
I just finished some HT on / HT off tests to see how things have changed in
Crafty since some of the recent NUMA-related memory changes that were made.
Point 1. HT now speeds Crafty up between 5 and 10% max. A year ago this was
30%. What did I learn? Nothing new. Memory waits benefit HT. Eugene and I
worked on removing several shared memory interactions which led to better cache
utilization, less cache invalidates (very slow) and improved performance a good
bit. But at the same time, now HT doesn't have the excessive memory waits it
had before and so the speedup is not as good.
Point 2. HT now actually slows things down due to SMP overhead. IE I lose 30%
per CPU, roughly, due to SMP overhead. HT now only gives 5-10% back. This is a
net loss. I am now running my dual with HT disabled...
More as I get more data... Here is two data points however:
pos1. cpus=2 (no HT) NPS = 2.07M time=18.13
cpus=4 NPS = 2.08M time=28.76
pos2. cpus=2 NPS = 1.87M time=58.48
cpus=4 NPS = 2.01M time=66.00
First pos HT helps almost none in NPS, costs 10 seconds in search overhead.
Ugly. Position 2 gives about 5% more nps, but again the SMP overhead washes
that out and there is a net loss. I should run the speedup tests several times,
but the NPS numbers don't change much, and the speedup could change. But this
offers enough..
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