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copied!<p>As a previous answer said, the rate at which <code>jiffies</code> increments is fixed.</p> <p>The standard way of specifying time for a function that accepts <code>jiffies</code> is using the constant <code>HZ</code>.</p> <p>That's the abbreviation for Hertz, or the number of ticks per second. On a system with a timer tick set to 1ms, HZ=1000. Some distributions or architectures may use another number (100 used to be common).</p> <p>The standard way of specifying a <code>jiffies</code> count for a function is using <code>HZ</code>, like this:</p> <pre><code>schedule_timeout(HZ / 10); /* Timeout after 1/10 second */ </code></pre> <p>In most simple cases, this works fine.</p> <pre><code>2*HZ /* 2 seconds in jiffies */ HZ /* 1 second in jiffies */ foo * HZ /* foo seconds in jiffies */ HZ/10 /* 100 milliseconds in jiffies */ HZ/100 /* 10 milliseconds in jiffies */ bar*HZ/1000 /* bar milliseconds in jiffies */ </code></pre> <p>Those last two have a bit of a problem, however, as on a system with a 10 ms timer tick, <code>HZ/100</code> is 1, and the precision starts to suffer. You may get a delay anywhere between 0.0001 and 1.999 timer ticks (0-2 ms, essentially). If you tried to use <code>HZ/200</code> on a 10ms tick system, the integer division gives you 0 jiffies!</p> <p>So the rule of thumb is, be very careful using HZ for tiny values (those approaching 1 jiffie).</p> <p>To convert the other way, you would use:</p> <pre><code>jiffies / HZ /* jiffies to seconds */ jiffies * 1000 / HZ /* jiffies to milliseconds */ </code></pre> <p>You shouldn't expect anything better than millisecond precision.</p>

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