On 2014-07-17 6:39 AM, Christian Quest wrote:
I'm currently doing some rendering benchmark to tune a new tile server
we're about to put online.
A strange thing I've found last night: render_list with 16 thread
takes more time than with 8 .
The server has 2 quad-core Xeon (X5570), this means 8 physical cores.
It looks like hyperthreading adds additionnal context switches or
something similar.
With "-z 9 -Z 9 -n 16 -l 32" it takes 3016s, and with "-z 9 -Z 9 -n 8
-l 12" 2647s, 10% less.
I'll disable HT on my next run in the server bios and see if it is
consistent.
Is there a chance you're running into IO bottlenecks?
Another thing I found... do not put your SSD behind a RAID card.
The RAID card (Dell Perc 6i) add too much latency.
On the same render_list, the iowait threads are increasing a lot and
iops decreases a lot.
The Perc 6 is an older lower-end RAID card using a LSI 10xx chip. It
doesn't surprise me it doesn't work ideally with SSDs. I'm also not sure
if it supports all the SATA commands a SSD uses, which can be a serious
issue for consistency, the bane of SSDs.
A more modern card would probably perform better, but if you're not
RAIDing SSDs, you should really be using any card you have in HBA mode,
unless you have a battery-backed cache and can therefor tune write
barriers and related settings better.
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