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.
--
Jens Axboe
--
To unsubscribe from this list: send the line "unsubscribe linux-doc" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
