<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hello Gaetan,<div><br></div><div>I was using SimpleITK to perform some basic operations on images and this filter was taking a significant amount of time by comparison. As I was waiting I looked at the code, and saw this issue.</div><div><br></div><div><br></div><div>I have seen talks on Intel Parallel Studio which includes a multi-threading profiling tool which can detect this type of thing, it's only for Visual Studio, and I am unaware of comparable open sour tools to analyze similar multi-threading issue.</div><div><br></div><div><br></div><div>Brad</div><div><br><div><div>On Mar 19, 2012, at 3:55 AM, Gaetan Lehmann wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div><br></div><div>Hi Brad,</div><div><br></div><div>This is very interesting.</div><div>Could you tell us what you have done to identify this problem?</div><div><br></div><div>Thanks,</div><div><br></div><div>Gaëtan</div>
<div><br></div><br><br><div class="gmail_quote">Le 16 mars 2012 21:59, Bradley Lowekamp <span dir="ltr"><<a href="mailto:blowekamp@mail.nih.gov">blowekamp@mail.nih.gov</a>></span> a écrit :<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word">After digging a little further I think this problem may better be called "False Sharing" and there is a wikipedia page about it:<div><a href="http://en.wikipedia.org/wiki/False_sharing" target="_blank">http://en.wikipedia.org/wiki/False_sharing</a></div>
<div><br></div><div>Additionally the common cache block size for intel processors is 64 words. And the caching protocols should maintain this consistently between processors if shared.<div><br></div><div>Brad</div><div><br>
<div><div><div class="h5"><div>On Mar 16, 2012, at 3:16 PM, Lowekamp, Bradley (NIH/NLM/LHC) [C] wrote:</div><br></div></div><blockquote type="cite"><div><div class="h5"><div style="word-wrap:break-word">Hello,<div><br></div>
<div>I have just made the StatisticsImageFilter go ~58X faster on my multi-core platform for large data, by fixing the cache thrashing which was going on:</div><div><br></div><div><a href="http://review.source.kitware.com/#/c/4771/1" target="_blank">http://review.source.kitware.com/#/c/4771/1</a></div>
<div><br></div><div>When adjacent memory is modified by different processors, it must maintain consistency across the cores. This is of non-trivial expense then considered on the per-pixel level. If anyone is looking for an example case of bad cache thrashing I think this it about as good as you can do.</div>
<div><br></div><div>I am just sending this e-mail to make sure everyone is on the look out for this type of problem, and will take a note (Jira?) of where similar enhancements can occur.</div><div><br></div><div><br></div>
<div>Thanks for keeping an eye out,</div><div>Brad</div><div><br><div>
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<font face="Helvetica" size="3" style="font:normal normal normal 12px/normal Helvetica">Bradley Lowekamp<span> </span><span> </span></font></div><div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px">
<font face="Helvetica" size="3" style="font:normal normal normal 12px/normal Helvetica">Medical Science and Computing for</font></div><div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px"><font face="Helvetica" size="3" style="font:normal normal normal 12px/normal Helvetica">Office of High Performance Computing and Communications</font></div>
<div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px"><font face="Helvetica" size="3" style="font:normal normal normal 12px/normal Helvetica">National Library of Medicine<span> </span></font></div>
<div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px"><font face="Helvetica" size="3" style="font:normal normal normal 12px/normal Helvetica"><a href="mailto:blowekamp@mail.nih.gov" target="_blank">blowekamp@mail.nih.gov</a></font></div>
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<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; -webkit-text-decorations-in-effect: none; text-indent: 0px; -webkit-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="3" style="font: normal normal normal 12px/normal Helvetica; ">========================================================</font></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="3" style="font: normal normal normal 12px/normal Helvetica; ">Bradley Lowekamp<span class="Apple-converted-space"> </span><span class="Apple-converted-space"> </span></font></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="3" style="font: normal normal normal 12px/normal Helvetica; ">Medical Science and Computing for</font></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="3" style="font: normal normal normal 12px/normal Helvetica; ">Office of High Performance Computing and Communications</font></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="3" style="font: normal normal normal 12px/normal Helvetica; ">National Library of Medicine<span class="Apple-converted-space"> </span></font></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><font face="Helvetica" size="3" style="font: normal normal normal 12px/normal Helvetica; "><a href="mailto:blowekamp@mail.nih.gov">blowekamp@mail.nih.gov</a></font></p><br class="Apple-interchange-newline"></span></div></span></span><br class="Apple-interchange-newline">
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