[CC'd to util-linux mailing list]
On 06/18/2012 09:28 PM, Jens Axboe wrote:
> On 06/18/2012 01:48 PM, Zheng Liu wrote:
>> Hi Jens,
>>
>> I meet a problem when I use ionice(1) to adjust a process's io priority.
>> I do the following operations:
>>
>> $ ionice -p${pid}
>> none: prio 0
>> $ ionice -p${pid} -c2 -n4
>> $ ionice -p${pid}
>> best-effort: prio 4
>> $ ionice -p${pid} -c0 -n0
>> $ ionice -p${pid}
>> best-effort: prio 0
>>
>> So I cannot set scheduling class back to 'none'. If I call ioprio_set(2)
>> directly, it will be fine. But if I use ionice(1), I cannot change it. I
>> read the docs about ionice in [1]. I notice this code:
>>
>> switch (ioprio_class) {
>> case IOPRIO_CLASS_NONE:
>> ioprio_class = IOPRIO_CLASS_BE;
>> ^^^^^^^^^^^^^^^^
>> *It means that we cannot set back to none.*
>> break;
>> case IOPRIO_CLASS_RT:
>> case IOPRIO_CLASS_BE:
>> break;
>> case IOPRIO_CLASS_IDLE:
>> ioprio = 7;
>> break;
>> default:
>> printf("bad prio class %d\n", ioprio_class);
>> return 1;
>> }
>>
>> My question is why we need to ban the user to set back to 'none'. Is there
>> some reasons? Thank you.
>
> The kernel code does allow it, so it's only in the tool that this
> restriction exists. I don't think we have a particularly good reason to
> have it there. This is a tools question, though, not a kernel issue. I
> suggest you take it up with the util-linux crew. I'm fine with removing
> this restriction from ionice, especially since you could just roll your
> own that did it.
>
Thanks for your reply. Hopefully we can get some feedbacks from
util-linux crew.
Regards,
Zheng
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