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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>Glossary</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="Unreliable Guide To Locking" /><link rel="up" href="index.html" title="Unreliable Guide To Locking" /><link rel="prev" href="ch12.html" title="Chapter 12. Thanks" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Glossary</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch12.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> </td></tr></table><hr /></div><div class="glossary" title="Glossary"><div class="titlepage"><div><div><h2 class="title"><a id="glossary"></a>Glossary</h2></div></div></div><dl><dt><a id="gloss-preemption"></a>preemption</dt><dd><p>
Prior to 2.5, or when <span class="symbol">CONFIG_PREEMPT</span> is
unset, processes in user context inside the kernel would not
preempt each other (ie. you had that CPU until you gave it up,
except for interrupts). With the addition of
<span class="symbol">CONFIG_PREEMPT</span> in 2.5.4, this changed: when
in user context, higher priority tasks can "cut in": spinlocks
were changed to disable preemption, even on UP.
</p></dd><dt><a id="gloss-bh"></a>bh</dt><dd><p>
Bottom Half: for historical reasons, functions with
'_bh' in them often now refer to any software interrupt, e.g.
<code class="function">spin_lock_bh()</code> blocks any software interrupt
on the current CPU. Bottom halves are deprecated, and will
eventually be replaced by tasklets. Only one bottom half will be
running at any time.
</p></dd><dt><a id="gloss-hwinterrupt"></a>Hardware Interrupt / Hardware IRQ</dt><dd><p>
Hardware interrupt request. <code class="function">in_irq()</code> returns
<span class="returnvalue">true</span> in a hardware interrupt handler.
</p></dd><dt><a id="gloss-interruptcontext"></a>Interrupt Context</dt><dd><p>
Not user context: processing a hardware irq or software irq.
Indicated by the <code class="function">in_interrupt()</code> macro
returning <span class="returnvalue">true</span>.
</p></dd><dt><a id="gloss-smp"></a><acronym class="acronym">SMP</acronym></dt><dd><p>
Symmetric Multi-Processor: kernels compiled for multiple-CPU
machines. (CONFIG_SMP=y).
</p></dd><dt><a id="gloss-softirq"></a>Software Interrupt / softirq</dt><dd><p>
Software interrupt handler. <code class="function">in_irq()</code> returns
<span class="returnvalue">false</span>; <code class="function">in_softirq()</code>
returns <span class="returnvalue">true</span>. Tasklets and softirqs
both fall into the category of 'software interrupts'.
</p><p>
Strictly speaking a softirq is one of up to 32 enumerated software
interrupts which can run on multiple CPUs at once.
Sometimes used to refer to tasklets as
well (ie. all software interrupts).
</p></dd><dt><a id="gloss-tasklet"></a>tasklet</dt><dd><p>
A dynamically-registrable software interrupt,
which is guaranteed to only run on one CPU at a time.
</p></dd><dt><a id="gloss-timers"></a>timer</dt><dd><p>
A dynamically-registrable software interrupt, which is run at
(or close to) a given time. When running, it is just like a
tasklet (in fact, they are called from the TIMER_SOFTIRQ).
</p></dd><dt><a id="gloss-up"></a><acronym class="acronym">UP</acronym></dt><dd><p>
Uni-Processor: Non-SMP. (CONFIG_SMP=n).
</p></dd><dt><a id="gloss-usercontext"></a>User Context</dt><dd><p>
The kernel executing on behalf of a particular process (ie. a
system call or trap) or kernel thread. You can tell which
process with the <span class="symbol">current</span> macro.) Not to
be confused with userspace. Can be interrupted by software or
hardware interrupts.
</p></dd><dt><a id="gloss-userspace"></a>Userspace</dt><dd><p>
A process executing its own code outside the kernel.
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