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I would be interested in testing<br />> > feedback. Patch is for 2.6.15.<br />> ><br />> > Optimize select and poll by a using stack space for small fd sets<br />> ><br />> > This brings back an old optimization from Linux 2.0. Using<br />> > the stack is faster than kmalloc. On a Intel P4 system<br />> > it speeds up a select of a single pty fd by about 13%<br />> > (~4000 cycles -> ~3500)<br />><br />> Was this result on UP or SMP kernel ? Preempt or not ?<br /><br />SMP kernel, non preempt, on a uniprocessor hyperthreaded CPU.<br /><br />><br />> I think we might play in do_pollfd() and use fget_light()/fput_light()<br />> instead of fget()/fput() that are somewhat expensive because of atomic<br />> inc/dec on SMP.<br /><br />One idea was to just cache the file references over multiple syscalls and only<br />free them using a timer or when some thread calls close().<br />This would also avoid taking the spinlocks to set up the wait queues.<br /><br />Then a new select or poll would just check if the input set matches<br />the caches and only fix up what changed.<br /><br />But i didn't implement this because I would be quite a bit more complicated<br />instead of this simple patch.<br /><br />><br />> (I believe that select()/poll() based daemons are mostly non<br />> multi-threaded, since high performance multi-threaded programs should be<br />> using epoll...)<br /><br />Yes, epoll should have a similar effect.<br /><br />-Andi<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: 2006-01-04 00:07 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>