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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I believe I’ve fixed the bug; it was actually more mundane than I guessed: the UMP stubs would send an ack for a received message before they had consumed the
message payload. <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">There are two patches attached:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">ump_flounder.patch fixes the broken logic in the stub compiler. It should be the only one you need.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">ump_support.patch fixes a minor unrelated problem I noticed while looking for the bug: the “next sequence ID” field was mislabelled and started from 0 rather
than 1. I believe this is independent of the previous patch, but since I’m testing with this code in my tree, I’m including it for completeness.<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">Please let me know how you go…<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Andrew<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>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Baumann Andrew
<br>
<b>Sent:</b> Wednesday, 18 January 2012 10:02<br>
<b>To:</b> 'Zeus Gómez Marmolejo'<br>
<b>Cc:</b> barrelfish-users@lists.inf.ethz.ch<br>
<b>Subject:</b> RE: [Barrelfish-users] Corruption sending buffer<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Hi Zeus,<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 was dubious, but you’re right, it really is broken. I’m amazed the rest of the system works as well as it does! :)<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">The good news, is that it’s not just random memory corruption. If I print out the expected and received value, it is always off by 32:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">expected 200711824 but got 200711856<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">expected 218117022 but got 218117054<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">expected 292546689 but got 292546721<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">expected 360468278 but got 360468310<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">expected 370495166 but got 370495198<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">expected 377519952 but got 377519984<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">expected 581714255 but got 581714287<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">expected 619853741 but got 619853773<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"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The default UMP channel length (which is chosen so as to fit two unidirectional channels in a 4k page) is 32 messages. I can’t see any pattern to when the incorrect
values arise (in the overall stream), so this suggests pretty strongly that there is a race condition occurring on wrap-around in the underlying channel. I’ll try to get to the bottom of it…<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">Andrew<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>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">
<a href="mailto:zeus@aluzina.org">zeus@aluzina.org</a> <a href="mailto:[mailto:zeus@aluzina.org]">
[mailto:zeus@aluzina.org]</a> <b>On Behalf Of </b>Zeus Gómez Marmolejo<br>
<b>Sent:</b> Tuesday, 17 January 2012 15:26<br>
<b>To:</b> Baumann Andrew<br>
<b>Cc:</b> <a href="mailto:barrelfish-users@lists.inf.ethz.ch">barrelfish-users@lists.inf.ethz.ch</a><br>
<b>Subject:</b> Re: [Barrelfish-users] Corruption sending buffer<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Ok,<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I've simplified the example even more. Now, there is no buffer sent. Only a uint32_t as a parameter of the message handler. Each time this integer is being incremented by 1. This keeps going till it aborts when the integer received by the
second core is not what it should be.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">As before, there are 2 cores, one sending and the other receiving with 1 thread per core. x86_64 is the architecture.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">This error prevents my benchmarks from running as I'm sending a lot of messages from one node to another and at some point it aborts because the gasnet handler index is not correct.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thanks for your help!<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">zeus.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">El 17 de enero de 2012 15:06, Zeus Gómez Marmolejo <<a href="mailto:zeus.gomez@bsc.es">zeus.gomez@bsc.es</a>> escribió:<o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt">Hi Andrew,<o:p></o:p></p>
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<p class="MsoNormal">El 16 de enero de 2012 20:58, Baumann Andrew <<a href="mailto:andrewb@inf.ethz.ch" target="_blank">andrewb@inf.ethz.ch</a>> escribió:<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"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Hi Zeus,</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">At first look your program appears to be correct if sizeof(unsigned) == 4 on both source and destination.
Although sending 4kB buffers through the IDC system in this way is madness, it should work.</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Yes, I forgot to say that the architecture I was running is x86_64. <o:p></o:p></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"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Unfortunately I’m not in a good position to run this right now (… it’s a long story involving snow
and an out-of-date QEMU). When it fails, is the incorrect value one from the previous iteration, or is it garbage?</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The incorrect value is 0 almost all the time is failing.<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"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">BTW, there is a minor use-after-free bug in your debug_printf() in the receive handler.</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">You are right, but placing the debug_printf() before the free() doesn't make the error go away.<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"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Andrew</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Zeus
Gómez Marmolejo [mailto:<a href="mailto:zeus.gomez@bsc.es" target="_blank">zeus.gomez@bsc.es</a>]
<br>
<b>Sent:</b> Monday, 16 January 2012 11:39<br>
<b>To:</b> <a href="mailto:barrelfish-users@lists.inf.ethz.ch" target="_blank">barrelfish-users@lists.inf.ethz.ch</a><br>
<b>Subject:</b> [Barrelfish-users] Corruption sending buffer</span><o:p></o:p></p>
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<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">Dear Barrelfish developers,<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">I believe that I've found a bug in the message passing interface when a buffer is sent between two endpoints. I would like you to have a look at this example I'm sending to you.
You can copy it to the folder "usr/tests/idctest" of the latest version of the public repository. It should build correctly.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">This is a very simple example: it has 2 cores, with one thread per core. Only one core is sending a message to the other core. The message is a simple buffer of 1024 unsigned integers
where the first integer and the last one is the same, it's incremented in each message sent. The message handler on the receiver is just checking that the first and the last integer of the buffer are the same.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">The application keeps running until it finds that the two integers differ. This means that the buffer has been sent incorrectly. I've tested this in qemu and in a real machine and
after a while the program aborts because of a corrupt buffer. In both systems, the error happens before 2 minutes approx.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Can you have a look at this example and check whether I'm doing something wrong? <br clear="all">
<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Many thanks!!<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt">-- <br>
Zeus Gómez Marmolejo<br>
Barcelona Supercomputing Center<br>
PhD student<br>
<a href="http://www.bsc.es" target="_blank">http://www.bsc.es</a><o:p></o:p></p>
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<p class="MsoNormal"><br>
<br clear="all">
<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="margin-bottom:12.0pt">-- <br>
Zeus Gómez Marmolejo<br>
Barcelona Supercomputing Center<br>
PhD student<br>
<a href="http://www.bsc.es" target="_blank">http://www.bsc.es</a><o:p></o:p></p>
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<p class="MsoNormal"><br>
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<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="margin-bottom:12.0pt">-- <br>
Zeus Gómez Marmolejo<br>
Barcelona Supercomputing Center<br>
PhD student<br>
<a href="http://www.bsc.es" target="_blank">http://www.bsc.es</a><o:p></o:p></p>
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