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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Thanks Sz</span><span lang="ES-AR" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">ilárd,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="ES-AR" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I understand. I am feeding this kernel for both architectures (ARM / NEON and x86 / AVX2) with the same input structures (initialized in the stack, I have replaced
the STL vectors for C-style arrays and I am aligning using alignas(X) keyword for GCC) :
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> // src/gromacs/nbnxm/atomdata.h -> src/nbnxb_class_t_new.h<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> </span><span lang="DE" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">const nbnxn_atomdata_t nbat;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="DE" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> // src/gromacs/nbnxm/pairlist.h -> src/NbnxnPairlistCpu_new.h<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="DE" style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"> </span><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">const NbnxnPairlistCpu nbl;<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">I suppose that for both architectures the results should be the same for the force vector in the output, right? Same input same output no matter the SIMD instructions
used, is that correct? Are these dummy particle defined in one of these two structures?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D">Cheers, Guido.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> gromacs.org_gmx-developers-bounces@maillist.sys.kth.se [mailto:gromacs.org_gmx-developers-bounces@maillist.sys.kth.se]
<b>On Behalf Of </b>Szilárd Páll<br>
<b>Sent:</b> Thursday, November 26, 2020 12:30 PM<br>
<b>To:</b> Discussion list for GROMACS development <gmx-developers@gromacs.org><br>
<b>Cc:</b> gmx-developers mailing list <gromacs.org_gmx-developers@maillist.sys.kth.se><br>
<b>Subject:</b> Re: [gmx-developers] 4xN kernel using Advanced NEON (VL=128 bits) and double-FP<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Thu, Nov 26, 2020, 9:25 AM Guido Giuntoli <<a href="mailto:guido.giuntoli@huawei.com">guido.giuntoli@huawei.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Hi,<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">I am building a minikernel of the 4 x N kernel and testing it in different architectures. Currently I am trying with in an ARMv8 with Advanced NEON using double-FP.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">I see that this kernel operates with 4 particles at the time. When I use double-FP I can fill each SIMD unit with 2 FP numbers (128 bits long for Advanced NEON). I checked that
that some interactions in this kernel between the 4 particles are not performed: particle 3 and 4 have net force = 0 (in this minikernel). Am I losing something here?
<o:p></o:p></p>
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<p class="MsoNormal">Not all interactions computed will evaluate to non-stop values.<o:p></o:p></p>
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<p class="MsoNormal">E.g. there could be "dummy" particles used for padding or ( depending on your inputs) part of excluded particles.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Arial",sans-serif">--<br>
Szilárd<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Is the kernel prepared to operate in double precision for vector lengths of 128 bits? Is the masking mechanism intended to solve this issue?<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Note: when I use single-FP the 4 forces are different from 0 as I expected.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Thanks a lot for the help ;)
<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span style="font-size:10.0pt;color:#666666">Best regards | Mit freundlichen Grüßen</span></b><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span style="font-size:10.0pt;color:#666666"> </span></b><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span style="font-size:10.0pt;color:#666666">Guido Giuntoli</span></b><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span style="font-size:10.0pt;color:#666666"> </span></b><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">HUAWEI TECHNOLOGIES Duesseldorf GmbH<br>
Hansaallee 205, 40549 Dusseldorf, Germany, <a href="http://www.huawei.com/" target="_blank">
<b>www.huawei.com</b></a><br>
Registered Office: Düsseldorf, Register Court Düsseldorf, HRB 56063, <br>
Managing Director: Li Peng, Li Jian, Shi Yanli<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="DE">Sitz der Gesellschaft: Düsseldorf, Amtsgericht Düsseldorf, HRB 56063,
<br>
Geschäftsführer: Li Peng, Li Jian, Shi Yanli</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span lang="EN-GB" style="font-size:9.0pt">-----------------------------------------------------------------------------------------------</span></b><o:p></o:p></p>
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