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    SubjectRe: [BUG] cpu-hotplug: Can't offline the CPU with naughty realtime processes
    On Tue, May 08, 2007 at 04:16:06PM +0900, Satoru Takeuchi wrote:
    > Sometimes I wonder at prio_array. It has 140 entries(from 0 to 139),
    > and the meaning of each entry is as follows, I think.
    >
    > +-----------+-----------------------------------------------+
    > | index | usage |
    > +-----------+-----------------------------------------------+
    > | 0 - 98 | RT processes are here. They are in the entry |
    > | | whose index is 99 - sched_priority. |

    From sched.h:

    /*
    * Priority of a process goes from 0..MAX_PRIO-1, valid RT
    * priority is 0..MAX_RT_PRIO-1, and SCHED_NORMAL/SCHED_BATCH
    * tasks are in the range MAX_RT_PRIO..MAX_PRIO-1.

    so shouldn't the index for RT processes be 0 - 99, given that
    MAX_RT_PRIO = 100?

    > +-----------+-----------------------------------------------+
    > | 99 | No one use it? CMIIW. |
    > +-----------+-----------------------------------------------+
    > | 100 - 139 | Ordinally processes are here. They are in the |
    > | | entry whose index is (nice+120) +/- 5 |
    > +-----------+-----------------------------------------------+
    >
    > What's the purpose of the prio_array[99]? Once I exlore source tree
    > briefly and can't found any kernel thread which uses this entry.
    > Does anybody know?

    --
    Regards,
    vatsa
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