Changes

The I/O priorities feature is implemented in OpenVZ since kernel <tt>2.6.18-028stable021</tt>, <tt>vzctl 3.0.16</tt>. This feature allows to assign I/O priority to any [[VEcontainer]]. Priority range is <tt>0-7</tt>. The more priority a [[VE]] container has, the more time for using block devices this [[VE]] container will obtain. Note, that this This feature is implemented based on base of CFQ I/O scheduler, so this scheduler should be used for block device in question. Default I/O priority is <tt>4</tt>. Examples of using:<pre> vzctl set 101 --ioprio 0 --save</pre><pre> vzctl set 101 --ioprio 7 --save</pre>The mapping from priority to time is the following: if <tt>0</tt> prio corresponds to time slice <tt>t</tt>, than <tt>8</tt> prio corresponds to time slice <tt>2 * t</tt>. Default time slice value is <tt>HZ/2</tt>. The main criteria for fairness at the moment is that if you set I/O prio of VE CT 1 to <tt>p1</tt> and I/O prio of VE CT 2 to <tt>p2</tt>, and <tt>p1 > p2</tt> then VE CT 1 should do more I/O than VE CT 2.