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<div class="moz-cite-prefix">On 2014-07-17 6:39 AM, Christian Quest
wrote:<br>
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<blockquote
cite="mid:CAAXY6DOXDuc_jrr09vZcwP=PY1CH5t4NU-g392__OVf4yPrUyA@mail.gmail.com"
type="cite">
<div dir="ltr">I'm currently doing some rendering benchmark to
tune a new tile server we're about to put online.<br clear="all">
<div><br>
</div>
<div>A strange thing I've found last night: render_list with 16
thread takes more time than with 8 .</div>
<div><br>
</div>
<div>The server has 2 quad-core Xeon (X5570), this means 8
physical cores. It looks like hyperthreading adds additionnal
context switches or something similar.</div>
<div>With "<span
style="color:rgb(0,0,0);font-family:arial,sans,sans-serif;font-size:100%">-z
9 -Z 9 -n 16 -l 32" it takes 3016s, and with "</span><span
style="color:rgb(0,0,0);font-family:arial,sans,sans-serif;font-size:13px;white-space:pre-wrap">-z
9 -Z 9 -n 8 -l 12" 2647s, 10% less.</span></div>
<div><span
style="color:rgb(0,0,0);font-family:arial,sans,sans-serif;font-size:13px;white-space:pre-wrap"><br>
</span></div>
<div><font color="#000000" face="arial, sans, sans-serif"><span
style="white-space:pre-wrap">I'll disable HT on my next
run in the server bios and see if it is consistent.</span></font></div>
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</blockquote>
<br>
Is there a chance you're running into IO bottlenecks?<br>
<br>
<blockquote
cite="mid:CAAXY6DOXDuc_jrr09vZcwP=PY1CH5t4NU-g392__OVf4yPrUyA@mail.gmail.com"
type="cite">
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<div><font color="#000000" face="arial, sans, sans-serif"><span
style="white-space:pre-wrap">Another thing I found... do
not put your SSD behind a RAID card.</span></font></div>
<div><font color="#000000" face="arial, sans, sans-serif"><span
style="white-space:pre-wrap">The RAID card (Dell Perc 6i)
add too much latency.</span></font></div>
<div><font color="#000000" face="arial, sans, sans-serif"><span
style="white-space:pre-wrap">On the same render_list, the
iowait threads are increasing a lot and iops decreases a
lot.</span></font></div>
</div>
</blockquote>
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.<br>
<br>
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.<br>
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