<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<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);">
Hello Phil,</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);">
> We use ABT_SCHED_BASIC_WAIT and ABT_POOL_FIFO_WAIT by default in Mochi (Margo). Even so, if the default (simple) mutex is busy-yielding, that will effectively become a busy spin if the ES has no other units to execute, right?
<div><br>
</div>
<div>If a ULT is waiting in a lock (e.g., ABT_mutex_lock() or ABT_rwlock_rwlock()), yes, you're right. Sorry for the confusing behavior. It should have been clarified somewhere.</div>
<div><br>
</div>
<span>This "default" behavior is only for a historical reason. If `--disable-simple-mutex` solves some performance issues (this configuration option works for Argobots 1.1), please let us know. I just need to change the default option for this.</span><br>
</div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<span><br>
</span></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<span>Thanks,</span></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<span>Shintaro</span></div>
<div style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div id="appendonsend"></div>
<hr style="display:inline-block;width:98%" tabindex="-1">
<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Phil Carns via discuss <discuss@lists.argobots.org><br>
<b>Sent:</b> Friday, July 23, 2021 12:25 PM<br>
<b>To:</b> Iwasaki, Shintaro via discuss <discuss@lists.argobots.org><br>
<b>Cc:</b> Carns, Philip H. <carns@mcs.anl.gov><br>
<b>Subject:</b> Re: [argobots-discuss] condition variable and rwlock</font>
<div> </div>
</div>
<div>
<p><br>
</p>
<div class="x_moz-cite-prefix">On 7/23/21 11:53 AM, Iwasaki, Shintaro via discuss wrote:<br>
</div>
<blockquote type="cite"><style type="text/css" style="display:none">
<!--
p
{margin-top:0;
margin-bottom:0}
-->
</style>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<div>Hi Matthieu,</div>
<div><br>
</div>
<div>By default, ABT_rwlock() and ABT_mutex() waits in a busy-yield loop (keeps yielding until a flag is set). If that configuration is set, waiters will suspend, not yield.</div>
</div>
</blockquote>
<p><br>
</p>
<p>I'm confused :)<br>
</p>
<p><br>
</p>
<p>We use ABT_SCHED_BASIC_WAIT and ABT_POOL_FIFO_WAIT by default in Mochi (Margo). Even so, if the default (simple) mutex is busy-yielding, that will effectively become a busy spin if the ES has no other units to execute, right?
<br>
</p>
<p><br>
</p>
<p>If so, that wasn't our intention. I thought that the ES would idle while trying to acquire an abt mutex if no other ULTs were runnable. We might need to do some testing to better understand what's going on there.</p>
<p><br>
</p>
<p>thanks,</p>
<p>-Phil<br>
</p>
<p><br>
</p>
<p><br>
</p>
<blockquote type="cite">
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<div><br>
</div>
<div>This behavior becomes default because of a historical reason (<a class="x_moz-txt-link-freetext" href="https://github.com/pmodels/argobots/pull/102">https://github.com/pmodels/argobots/pull/102</a>). There's a performance trade-off between a simple mutex
(current default) and a non-simple mutex, so we hesitate to change it silently.</div>
<div><br>
</div>
<div>If this default behavior is not what the user expects, I will create a PR to change it (if so I'd be happy if you create a GitHub issue that briefly describes this issue). </div>
<div><br>
</div>
<div>Thanks,</div>
<span>Shintaro</span><br>
</div>
<hr tabindex="-1" style="display:inline-block; width:98%">
<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Dorier, Matthieu
<a class="x_moz-txt-link-rfc2396E" href="mailto:mdorier@anl.gov"><mdorier@anl.gov></a><br>
<b>Sent:</b> Friday, July 23, 2021 10:34 AM<br>
<b>To:</b> <a class="x_moz-txt-link-abbreviated" href="mailto:discuss@lists.argobots.org">
discuss@lists.argobots.org</a> <a class="x_moz-txt-link-rfc2396E" href="mailto:discuss@lists.argobots.org">
<discuss@lists.argobots.org></a>; Iwasaki, Shintaro <a class="x_moz-txt-link-rfc2396E" href="mailto:siwasaki@anl.gov">
<siwasaki@anl.gov></a><br>
<b>Subject:</b> Re: condition variable and rwlock</font>
<div> </div>
</div>
<div>
<div dir="auto" style="direction:ltr; margin:0; padding:0; font-family:sans-serif; font-size:11pt; color:black">
Thanks, I'm curious about your comment about --disable-simple-mutex. What you describe is what I would expect rwlock to do by default... How do rwlock by default, then?<br>
<br>
</div>
<div dir="auto" style="direction:ltr; margin:0; padding:0; font-family:sans-serif; font-size:11pt; color:black">
Thanks<br>
</div>
<div dir="auto" style="direction:ltr; margin:0; padding:0; font-family:sans-serif; font-size:11pt; color:black">
Matthieu<span id="x_x_ms-outlook-android-cursor"></span><br>
<br>
</div>
<div dir="auto" style="direction:ltr; margin:0; padding:0; font-family:sans-serif; font-size:11pt; color:black">
<span id="x_x_OutlookSignature">
<div dir="auto" style="direction:ltr; margin:0; padding:0; font-family:sans-serif; font-size:11pt; color:black">
Get <a href="https://aka.ms/ghei36">Outlook for Android</a></div>
</span><br>
</div>
<hr tabindex="-1" style="display:inline-block; width:98%">
<div id="x_x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Iwasaki, Shintaro
<a class="x_moz-txt-link-rfc2396E" href="mailto:siwasaki@anl.gov"><siwasaki@anl.gov></a><br>
<b>Sent:</b> Friday, July 23, 2021 3:51:21 PM<br>
<b>To:</b> <a class="x_moz-txt-link-abbreviated" href="mailto:discuss@lists.argobots.org">
discuss@lists.argobots.org</a> <a class="x_moz-txt-link-rfc2396E" href="mailto:discuss@lists.argobots.org">
<discuss@lists.argobots.org></a>; Dorier, Matthieu <a class="x_moz-txt-link-rfc2396E" href="mailto:mdorier@anl.gov">
<mdorier@anl.gov></a><br>
<b>Subject:</b> Re: condition variable and rwlock</font>
<div> </div>
</div>
<style type="text/css" style="display:none">
<!--
p
{margin-top:0;
margin-bottom:0}
-->
</style>
<div dir="ltr">
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
Hello Matthieu,</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)">
Thanks for your question!</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)">
> Is there a way of using an Argobots condition variable with an rwlock instead of a mutex?<br>
</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
No. The user cannot combine ABT_rwlock with ABT_cond.</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)">
> my use-case is a structure that receives many read requests and a few writes, clearly justifying using a rwlock instead of a mutex, but I may want some of the reads to block until a write has happened, which means I need a condition variable
<div><br>
</div>
<div>First, if readers encounter an rwlock locked by a writer, they will suspend until the writer releases the rwlock (if --disable-simple-mutex is set, which is not set by default).</div>
<div><br>
</div>
<div>For this specific purpose(especially if "some", not "all" of the readers should block), what I came up with in my mind first is the following. It looks fine except for a seemingly complex structure that uses multiple synchronization objects.</div>
<div>
<div><br>
</div>
<div>void reader() {</div>
<div> while (1) {</div>
<div> if (work_queue.is_empty() and I_AM_SOME_OF_READERS()) {</div>
<div> // 1. Internally ABT_self_suspend()-like mechanism needs</div>
<div> // to take a lock (even if it is in the readers' lock)</div>
<div> // since multiple readers might access the same data</div>
<div> // structure (for example, a user-maintained</div>
<div> // suspended ULT list).</div>
<div> // 2. Anyway this path is not performance sensitive</div>
<div> ABT_mutex_lock(mutex);</div>
<div> ABT_cond_wait(cond, mutex);</div>
<div> ABT_mutex_unlock(mutex);</div>
<div> // Now someone woke me up after pushing work.</div>
<div> }</div>
<div> ABT_rwlock_rdlock(rwlock);</div>
<div> if (!work_queue.is_empty())</div>
<div> ; // Do real work.</div>
<div> ABT_rwlock_unlock(rwlock);</div>
<div> }</div>
<div>}</div>
<div><br>
</div>
<div>void writer() {</div>
<div> ABT_rwlock_wrlock(rwlock);</div>
<div> work_queue.push_work(work);</div>
<div> // You do not need to take a mutex to call ABT_cond_broadcast.</div>
<div> // It is fine even if there's no waiter.</div>
<div> ABT_cond_broadcast(cond);</div>
<div> ABT_rwlock_unlock(rwlock);</div>
<span>}</span><br>
</div>
<div><br>
</div>
</div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<span>I would welcome any suggestions! (For example, does ABT_rwlock_trywrlock() help?)<br>
</span></div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<span><br>
</span></div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<span>Best,</span></div>
<div style="font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt; color:rgb(0,0,0)">
<span>Shintaro</span></div>
<hr tabindex="-1" style="display:inline-block; width:98%">
<div id="x_x_x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> Dorier, Matthieu via discuss
<a class="x_moz-txt-link-rfc2396E" href="mailto:discuss@lists.argobots.org"><discuss@lists.argobots.org></a><br>
<b>Sent:</b> Friday, July 23, 2021 5:03 AM<br>
<b>To:</b> <a class="x_moz-txt-link-abbreviated" href="mailto:discuss@argobots.org">
discuss@argobots.org</a> <a class="x_moz-txt-link-rfc2396E" href="mailto:discuss@argobots.org">
<discuss@argobots.org></a><br>
<b>Cc:</b> Dorier, Matthieu <a class="x_moz-txt-link-rfc2396E" href="mailto:mdorier@anl.gov">
<mdorier@anl.gov></a><br>
<b>Subject:</b> [argobots-discuss] condition variable and rwlock</font>
<div> </div>
</div>
<style>
<!--
@font-face
{font-family:"Cambria Math"}
@font-face
{font-family:Calibri}
p.x_x_x_x_MsoNormal, li.x_x_x_x_MsoNormal, div.x_x_x_x_MsoNormal
{margin:0cm;
font-size:12.0pt;
font-family:"Calibri",sans-serif}
span.x_x_x_x_EmailStyle17
{font-family:"Calibri",sans-serif;
color:windowtext}
.x_x_x_x_MsoChpDefault
{font-size:12.0pt;
font-family:"Calibri",sans-serif}
-->
</style>
<div lang="EN-GB" style="word-wrap:break-word">
<div class="x_x_x_x_WordSection1">
<p class="x_x_x_x_MsoNormal"><span lang="EN-US" style="font-size:11.0pt">Hi,</span></p>
<p class="x_x_x_x_MsoNormal"><span lang="EN-US" style="font-size:11.0pt"> </span></p>
<p class="x_x_x_x_MsoNormal"><span lang="EN-US" style="font-size:11.0pt">I suspect the answer is no, but is there a way of using an Argobots condition variable with an rwlock instead of a mutex?</span></p>
<p class="x_x_x_x_MsoNormal"><span lang="EN-US" style="font-size:11.0pt">(my use-case is a structure that receives many read requests and a few writes, clearly justifying using a rwlock instead of a mutex, but I may want some of the reads to block until a write
has happened, which means I need a condition variable).</span></p>
<p class="x_x_x_x_MsoNormal"><span lang="EN-US" style="font-size:11.0pt">Thanks,</span></p>
<p class="x_x_x_x_MsoNormal"><span lang="EN-US" style="font-size:11.0pt"> </span></p>
<p class="x_x_x_x_MsoNormal"><span lang="EN-US" style="font-size:11.0pt">Matthieu
</span></p>
</div>
</div>
</div>
</div>
<br>
<fieldset class="x_mimeAttachmentHeader"></fieldset>
<pre class="x_moz-quote-pre">_______________________________________________
discuss mailing list
<a class="x_moz-txt-link-abbreviated" href="mailto:discuss@lists.argobots.org">discuss@lists.argobots.org</a>
<a class="x_moz-txt-link-freetext" href="https://lists.argobots.org/mailman/listinfo/discuss">https://lists.argobots.org/mailman/listinfo/discuss</a>
</pre>
</blockquote>
</div>
</body>
</html>