<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=Windows-1252">
<style type="text/css" style="display:none;"> P {margin-top:0;margin-bottom:0;} </style>
</head>
<body dir="ltr">
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div id="appendonsend"></div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
I read that out-of-order cores are supported. How about in-order cores? Would it be easy/difficult to add support for that?</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<br>
</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
Cheers,</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
Sjoerd.</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<br>
</div>
<hr tabindex="-1" style="display:inline-block; width:98%">
<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> llvm-dev <llvm-dev-bounces@lists.llvm.org> on behalf of Matt Davis via llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Sent:</b> 02 May 2019 19:59<br>
<b>To:</b> Shoaib Meenai; lorenzo chelini; llvm-dev@lists.llvm.org<br>
<b>Subject:</b> Re: [llvm-dev] Llvm-mca library.</font>
<div> </div>
</div>
<div lang="EN-US">
<div class="x_WordSection1">
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
Hi Lorenzo,</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
I’ll answer the first question you have:</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<span style="font-family:"Helvetica Neue"">> I would like to use llvm-mca to estimate the IPC of a given code region. I am interested in the library version (<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D50929-3Fid-3D162210&d=DwMFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=Ehy5cbFrTOTrtNpj4jTjwnMXspCxyoUuKpn3m8pxGpg&s=iEwPb0T8FqcGV-IscWqa3SAw64L-buGNLYvMLOgWoi4&e=">https://reviews.llvm.org/D50929?id=162210</a>)
but I have troubles understanding how to use it. Could you please point me to some documentations or (better) some code examples if any?</span></p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
The best example of the llvm-mca library being used is the actual llvm-mca tool itself. If you look in llvm/tools/llvm-mca/llvm-mca.cpp you’ll see that it is just a large program that uses the llvm-mca API and library. You’ll want to look at main() where
the default pipline is created and the viewers are associated to that pipeline instance.</p>
<ol start="1" type="1" style="margin-bottom: 0in;margin-top:0in">
<li class="x_MsoListParagraph" style="margin: 0in 0in 0.0001pt 0.5in; font-size: 11pt; font-family: Calibri, sans-serif;margin-left:0in">
You’ll need to construct an mca::Context and use that to create a mca::Pipeline instance. For starters, I suggest just using the default “out-of-order” pipeline. “createDefaultPipeline”</li><li class="x_MsoListParagraph" style="margin: 0in 0in 0.0001pt 0.5in; font-size: 11pt; font-family: Calibri, sans-serif;margin-left:0in">
Next, register some handlers take a look at the HWEventListener class in include/llvm/MCA. Use “Pipeline::addEventListener” to register for the events you might be interested in, such as pipeline stalls.</li></ol>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;margin-left:.5in">
llvm-mca.cpp does this on behalf of the Viewers. If you trace what the viewers are doing in the source file, you’ll probably</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;margin-left:.5in">
want to do something similar. </p>
<ol start="3" type="1" style="margin-bottom: 0in;margin-top:0in">
<li class="x_MsoListParagraph" style="margin: 0in 0in 0.0001pt 0.5in; font-size: 11pt; font-family: Calibri, sans-serif;margin-left:0in">
Call “Pipeline::run” to start your experiment and collect performance information.</li></ol>
<p class="x_MsoListParagraph" style="margin: 0in 0in 0.0001pt 0.5in; font-size: 11pt; font-family: Calibri, sans-serif;">
</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
Your second question:</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<span style="font-family:"Helvetica Neue"">> Reading the documentation (<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_docs_CommandGuide_llvm-2Dmca.html&d=DwMFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=Ehy5cbFrTOTrtNpj4jTjwnMXspCxyoUuKpn3m8pxGpg&s=5845DcPA4uSN_lgPE_SlH6XwRSShIfPIvYR1t8AZHpU&e=">https://llvm.org/docs/CommandGuide/llvm-mca.html</a>)
it also seems that llvm-mca does not take into account the cache hierarchy. Does this mean that the tool assumes all the loads/stores hit the L1 cache?</span></p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
As you pointed out, MCA does not really model the cache hierarchy. You might want to take a look at the Load/Store unit documentation as well:
<a href="http://llvm.org/doxygen/classllvm_1_1mca_1_1LSUnit.html">http://llvm.org/doxygen/classllvm_1_1mca_1_1LSUnit.html</a></p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
You probably already saw this from the CommandGuide for llvm-mca, but I’ll repeat it here:</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
“The LSUnit does not attempt to predict if a load or store hits or misses the L1 cache. It only knows if an instruction “MayLoad” and/or “MayStore.” For loads, the scheduling model provides an “optimistic” load-to-use latency (which usually matches the load-to-use
latency for when there is a hit in the L1D).”</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
Hope that helps,</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
-Matt</p>
<p class="x_MsoListParagraph" style="margin: 0in 0in 0.0001pt 0.5in; font-size: 11pt; font-family: Calibri, sans-serif;margin-left:0in">
<span style="font-size:10.5pt; font-family:"Lucida Grande",sans-serif; color:black; background:white"> </span></p>
<p class="x_MsoListParagraph" style="margin: 0in 0in 0.0001pt 0.5in; font-size: 11pt; font-family: Calibri, sans-serif;margin-left:0in">
</p>
<div style="border:none; border-top:solid #B5C4DF 1.0pt; padding:3.0pt 0in 0in 0in">
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<b><span style="font-size:12.0pt; color:black">From: </span></b><span style="font-size:12.0pt; color:black">Shoaib Meenai <smeenai@fb.com><br>
<b>Date: </b>Thursday, May 2, 2019 at 11:34 AM<br>
<b>To: </b>lorenzo chelini <l.chelini@icloud.com>, "llvm-dev@lists.llvm.org" <llvm-dev@lists.llvm.org>, Matt Davis <nullptr@fb.com><br>
<b>Subject: </b>Re: [llvm-dev] Llvm-mca library.</span></p>
</div>
<div>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
</p>
</div>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
(Adding Matt Davis, who should be able to help out here.)</p>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
</p>
<div style="border:none; border-top:solid #B5C4DF 1.0pt; padding:3.0pt 0in 0in 0in">
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<b><span style="font-size:12.0pt; color:black">From: </span></b><span style="font-size:12.0pt; color:black">llvm-dev <llvm-dev-bounces@lists.llvm.org> on behalf of lorenzo chelini via llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Reply-To: </b>lorenzo chelini <l.chelini@icloud.com><br>
<b>Date: </b>Thursday, May 2, 2019 at 4:15 AM<br>
<b>To: </b>"llvm-dev@lists.llvm.org" <llvm-dev@lists.llvm.org><br>
<b>Subject: </b>[llvm-dev] Llvm-mca library.</span></p>
</div>
<div>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
</p>
</div>
<div>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<span style="font-family:"Helvetica Neue"">Hi All,</span></p>
</div>
<div>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<span style="font-family:"Helvetica Neue""> </span></p>
</div>
<div>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<span style="font-family:"Helvetica Neue"">I would like to use llvm-mca to estimate the IPC of a given code region. I am interested in the library version (<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D50929-3Fid-3D162210&d=DwMFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=Ehy5cbFrTOTrtNpj4jTjwnMXspCxyoUuKpn3m8pxGpg&s=iEwPb0T8FqcGV-IscWqa3SAw64L-buGNLYvMLOgWoi4&e=">https://reviews.llvm.org/D50929?id=162210</a>)
but I have troubles understanding how to use it. Could you please point me to some documentations or (better) some code examples if any?</span></p>
</div>
<div>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<span style="font-family:"Helvetica Neue""> </span></p>
</div>
<div>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<span style="font-family:"Helvetica Neue"">Reading the documentation (<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_docs_CommandGuide_llvm-2Dmca.html&d=DwMFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=Ehy5cbFrTOTrtNpj4jTjwnMXspCxyoUuKpn3m8pxGpg&s=5845DcPA4uSN_lgPE_SlH6XwRSShIfPIvYR1t8AZHpU&e=">https://llvm.org/docs/CommandGuide/llvm-mca.html</a>)
it also seems that llvm-mca does not take into account the cache hierarchy. Does this mean that the tool assumes all the loads/stores hit the L1 cache?</span></p>
</div>
<div>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<span style="font-family:"Helvetica Neue""> </span></p>
</div>
<div>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<span style="font-family:"Helvetica Neue"">Looking forward to hearing from you.</span></p>
</div>
<div>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<span style="font-family:"Helvetica Neue"">Best regards,</span></p>
</div>
<div>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<span style="font-family:"Helvetica Neue""> </span></p>
</div>
<div>
<p class="x_MsoNormal" style="margin: 0in 0in 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif;">
<span style="font-family:"Helvetica Neue"">Lorenzo Chelini.</span></p>
</div>
</div>
</div>
</body>
</html>