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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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