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<?xml version="1.0" encoding="UTF-8" standalone="yes"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>LKML: Nick Piggin: Re: [PATCH 1/19] MUTEX: Introduce simple mutex implementation</title><link href="/css/message.css" rel="stylesheet" type="text/css" /><link href="/css/wrap.css" rel="alternate stylesheet" type="text/css" title="wrap" /><link href="/css/nowrap.css" rel="stylesheet" type="text/css" title="nowrap" /><link href="/favicon.ico" rel="shortcut icon" /><script src="/js/simple-calendar.js" type="text/javascript"></script><script src="/js/styleswitcher.js" type="text/javascript"></script><link rel="alternate" type="application/rss+xml" title="lkml.org : last 100 messages" href="/rss.php" /><link rel="alternate" type="application/rss+xml" title="lkml.org : last messages by Nick Piggin" href="/groupie.php?aid=29547" /><script> var _paq = window._paq = window._paq || []; /* tracker methods like "setCustomDimension" should be called before "trackPageView" */ _paq.push(["setDoNotTrack", true]); _paq.push(["disableCookies"]); _paq.push(['trackPageView']); _paq.push(['enableLinkTracking']); (function() { var u="//m.lkml.org/"; _paq.push(['setTrackerUrl', u+'matomo.php']); _paq.push(['setSiteId', '1']); var d=document, g=d.createElement('script'), s=d.getElementsByTagName('script')[0]; g.async=true; g.src=u+'matomo.js'; s.parentNode.insertBefore(g,s); })(); </script></head><body onload="es.jasper.simpleCalendar.init();" itemscope="itemscope" itemtype="http://schema.org/BlogPosting"><table border="0" cellpadding="0" cellspacing="0"><tr><td width="180" align="center"><a href="/"><img style="border:0;width:135px;height:32px" src="/images/toprowlk.gif" alt="lkml.org" /></a></td><td width="32">聽</td><td class="nb"><div><a class="nb" href="/lkml"> [lkml]</a> 聽 <a class="nb" href="/lkml/2005"> [2005]</a> 聽 <a class="nb" href="/lkml/2005/12"> [Dec]</a> 聽 <a class="nb" href="/lkml/2005/12/15"> [15]</a> 聽 <a class="nb" href="/lkml/last100"> [last100]</a> 聽 <a href="/rss.php"><img src="/images/rss-or.gif" border="0" alt="RSS Feed" /></a></div><div>Views: <a href="#" class="nowrap" onclick="setActiveStyleSheet('wrap');return false;">[wrap]</a><a href="#" class="wrap" onclick="setActiveStyleSheet('nowrap');return false;">[no wrap]</a> 聽 <a class="nb" href="/lkml/mheaders/2005/12/15/427" onclick="this.href='/lkml/headers'+'/2005/12/15/427';">[headers]</a>聽 <a href="/lkml/bounce/2005/12/15/427">[forward]</a>聽 </div></td><td width="32">聽</td></tr><tr><td valign="top"><div class="es-jasper-simpleCalendar" baseurl="/lkml/"></div><div class="threadlist">Messages in this thread</div><ul class="threadlist"><li class="root"><a href="/lkml/2005/12/12/244">First message in thread</a></li><li><a href="/lkml/2005/12/14/102">Arjan van de Ven</a><ul><li><a href="/lkml/2005/12/14/106">Andi Kleen</a><ul><li><a href="/lkml/2005/12/14/109">Arjan van de Ven</a></li></ul></li><li><a href="/lkml/2005/12/14/110">David Howells</a><ul><li><a href="/lkml/2005/12/14/116">Jakub Jelinek</a></li><li class="origin"><a href="/lkml/2005/12/16/43">Nick Piggin</a><ul><li><a href="/lkml/2005/12/16/43">David Howells</a><ul><li><a href="/lkml/2005/12/16/45">David Howells</a></li><li><a href="/lkml/2005/12/16/88">Nick Piggin</a></li><li><a href="/lkml/2005/12/16/156">Linus Torvalds</a></li></ul></li></ul></li></ul></li></ul></li></ul></td><td width="32" rowspan="2" class="c" valign="top"><img src="/images/icornerl.gif" width="32" height="32" alt="/" /></td><td class="c" rowspan="2" valign="top" style="padding-top: 1em"><table><tr><td><table><tr><td class="lp">Date</td><td class="rp" itemprop="datePublished">Fri, 16 Dec 2005 12:54:29 +1100</td></tr><tr><td class="lp">From</td><td class="rp" itemprop="author">Nick Piggin <></td></tr><tr><td class="lp">Subject</td><td class="rp" itemprop="name">Re: [PATCH 1/19] MUTEX: Introduce simple mutex implementation</td></tr></table></td><td></td></tr></table><pre itemprop="articleBody">David Howells wrote:<br />> Arjan van de Ven <arjan@infradead.org> wrote:<br />> <br />> <br />>>> given that<br />>>>mutex_down() is slightly more costly than current down(), and mutex_up() is<br />>>>appreciably more costly than current up()?<br />>><br />>>that's an implementation flaw in the current implementation that is not<br />>>needed by any means and that Ingo has fixed in his version of this<br />> <br />> <br />> As do I. I wrote it yesterday with Ingo looking over my shoulder, as it were,<br />> but I haven't released it yet.<br />> <br />> What I provided was a base implementation that anything can use provided it<br />> has an atomic op capable of exchanging between two states, and I suspect<br />> everything that can do multiprocessing has - if you can do spinlocks, then you<br />> can do this. I ALSO provided a mechanism by which it could be overridden if<br />> there's something better available on that arch.<br />> <br />> As I see it there are four classes of arch:<br />> <br />> (0) Those that have no atomic ops at all - in which case xchg is trivially<br />> implemented by disabling interrupts, and spinlocks must be null because<br />> they can't be implemented.<br />> <br />> (1) Those that only have a limited exchange functionality. Several archs do<br />> fall into this category: arm, frv, mn10300, 68000, i386.<br />> <br />> (2) Those that have CMPXCHG or equivalent: 68020, i486+, x86_64, ia64, sparc.<br />> <br />> (3) Those that have LL/SC or equivalent: mips (some), alpha, powerpc, arm6.<br />> <br /><br />cmpxchg is basically exactly equivalent to a store-conditional, so 2 and 3<br />are the same level.<br /><br />I don't know why you don't implement a "good" default implementation with<br />atomic_cmpxchg.<br /><br />-- <br />SUSE Labs, Novell Inc.<br /><br />Send instant messages to your online friends <a href="http://au.messenger.yahoo.com">http://au.messenger.yahoo.com</a> <br /><br />-<br />To unsubscribe from this list: send the line "unsubscribe linux-kernel" in<br />the body of a message to majordomo@vger.kernel.org<br />More majordomo info at <a href="http://vger.kernel.org/majordomo-info.html">http://vger.kernel.org/majordomo-info.html</a><br />Please read the FAQ at <a href="http://www.tux.org/lkml/">http://www.tux.org/lkml/</a><br /><br /></pre></td><td width="32" rowspan="2" class="c" valign="top"><img src="/images/icornerr.gif" width="32" height="32" alt="\" /></td></tr><tr><td align="right" valign="bottom"> 聽 </td></tr><tr><td align="right" valign="bottom">聽</td><td class="c" valign="bottom" style="padding-bottom: 0px"><img src="/images/bcornerl.gif" width="32" height="32" alt="\" /></td><td class="c">聽</td><td class="c" valign="bottom" style="padding-bottom: 0px"><img src="/images/bcornerr.gif" width="32" height="32" alt="/" /></td></tr><tr><td align="right" valign="top" colspan="2"> 聽 </td><td class="lm">Last update: 2005-12-16 02:57 聽聽 [from the cache]<br />漏2003-2020 <a href="http://blog.jasper.es/"><span itemprop="editor">Jasper Spaans</span></a>|hosted at <a href="https://www.digitalocean.com/?refcode=9a8e99d24cf9">Digital Ocean</a> and my Meterkast|<a href="http://blog.jasper.es/categories.html#lkml-ref">Read the blog</a></td><td>聽</td></tr></table><script language="javascript" src="/js/styleswitcher.js" type="text/javascript"></script></body></html>