<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"> <HTML ><HEAD ><TITLE >Big Reader Locks</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK REL="HOME" TITLE="Unreliable Guide To Locking" HREF="book1.html"><LINK REL="UP" TITLE="Common Techniques" HREF="c196.html"><LINK REL="PREVIOUS" TITLE="Per-CPU Data" HREF="x250.html"><LINK REL="NEXT" TITLE="Avoiding Locks: Read And Write Ordering" HREF="x261.html"></HEAD ><BODY CLASS="SECT1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >Unreliable Guide To Locking</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="x250.html" ACCESSKEY="P" ><<< Previous</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >Common Techniques</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="x261.html" ACCESSKEY="N" >Next >>></A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="BRLOCK" ></A >Big Reader Locks</H1 ><P > A classic example of per-CPU information is Ingo's `big reader' locks (<TT CLASS="FILENAME" >linux/include/brlock.h</TT >). These use the Per-CPU Data techniques described above to create a lock which is very fast to get a read lock, but agonizingly slow for a write lock. </P ><P > Fortunately, there are a limited number of these locks available: you have to go through a strict interview process to get one. </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="x250.html" ACCESSKEY="P" ><<< Previous</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="book1.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="x261.html" ACCESSKEY="N" >Next >>></A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Per-CPU Data</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="c196.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Avoiding Locks: Read And Write Ordering</TD ></TR ></TABLE ></DIV ></BODY ></HTML >