OSDI/Chapter/Chapter2/8Problems.html at master · Angold-4/OSDI · GitHub

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<nav id="TOC" role="doc-toc">
<ul>
<li><a href="#operating-systems-design-and-implementation-notes"
id="toc-operating-systems-design-and-implementation-notes">Operating
Systems Design and Implementation Notes</a></li>
<li><a href="#problems-of-chapter-2" id="toc-problems-of-chapter-2">8.
Problems of Chapter 2</a>
<ul>
<li><a href="#questions" id="toc-questions">Questions</a></li>
</ul></li>
</ul>
</nav>
<h2 id="operating-systems-design-and-implementation-notes">Operating
Systems Design and Implementation Notes</h2>
<h1 id="problems-of-chapter-2">8. Problems of Chapter 2</h1>
<h5 id="by-jiawei-wang">By Jiawei Wang</h5>
<h2 id="questions">Questions</h2>
<blockquote>
<p><strong>On all current computers, at least part of the interrupt
handlers are written in assembly language. Why?</strong></p>
</blockquote>
<p><strong>Generally, high level languages do not allow one the kind of
access to CPU hardware that is required. For instance, an interrupt
handler may be required to enable and disable the interrupt servicing a
particular device, or to manipulate data within a process’ stack area.
Also, interrupt service routines must execute as rapidly as
possible.</strong><br></p>
<blockquote>
<p><strong>What is the fundamental difference between a process and a
thread?</strong></p>
</blockquote>
<ul>
<li><strong>A process is a grouping of resources: an address space, open
files, signal handlers, and one or more threads.</strong></li>
<li><strong>A thread is just an execution unit.</strong><br></li>
</ul>
<blockquote>
<p><strong>In a system with threads, is there normally one stack per
thread or one stack per process? Explain.</strong></p>
</blockquote>
<p><strong>Each thread calls procedures on its own, so it must have its
own stack for the local variables, return addresses, and so
on.</strong><br></p>
<blockquote>
<p><strong>What is a race condition?</strong></p>
</blockquote>
<p><strong>A race condition is a situation in which two (or more)
process are about to perform some action. Depending on the exact timing,
one or other goes first. If one of the processes goes first, everything
works, but if another one goes first, a fatal error
occurs.</strong><br></p>
<blockquote>
<p><strong>Round-robin schedulers normally maintain a list of all
runnable processes, with each process occurring exactly once in the
list. What would happen if a process occurred twice in the list? Can you
think of any reason for allowing this?</strong></p>
</blockquote>
<p><strong>If a process occurs multiple times in the list, it will get
multiple quanta per cycle. This approach could be used to give more
important processes a larger share of the CPU.</strong><br></p>
<blockquote>
<p><strong>During execution, MINIX 3 maintains a variable proc ptr that
points to the process table entry for the current process.
Why?</strong></p>
</blockquote>
<p><strong>This pointer makes it easy to find the place to save the
registers when a process switch is needed, either due to a system call
or an interrupt.</strong><br></p>
<blockquote>
<p><strong>MINIX 3 does not buffer messages. Explain how this design
decision causes problems with clock and keyboard
interrupts.</strong></p>
</blockquote>
<p><strong>When a clock or keyboard interrupt occurs, and the task that
should get the message is not blocked, the system has to do something
strange to avoid losing the interrupt. With buffered messages this
problem would not occur. Notification bitmaps provide provide a simple
alternative to buffering.</strong></p>
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