ionice in FreeBSD?

[Jordi Espasa Clofent]

On 02/03/2010 12:12 PM, Bruce Simpson wrote:
> On 02/02/2010 17:19, Jordi Espasa Clofent wrote:
>>
>> In FreeBSD we've nice(1), renice(8) and even rtprio, idprio(1) but if
>> I'm understanding correctly, they're related to CPU priorty only, not
>> to I/O.
>
> That's not entirely true.
>
> A thread's CPU priority is still going to affect its ability to be
> scheduled on the CPU, and if it's waiting in the read() or write()
> syscalls, then this will make a difference to how quickly it can
> complete the next call.

Yes. I've already supposed it.

> However, it doesn't explicitly affect relative I/O prioritization. This
> is another story entirely. I suspect in a lot of cases adding a weight
> to per thread I/O, isn't going to make much difference for disk I/Os
> which are being sorted for the geometry (e.g. AHCI NCQ).
>
> So I guess my question is, 'why do you need I/O scheduling, and what
> aspect of system performance are you trying to solve with it' ?

Some shell-scripts based on dd or rsync, for example. Even a daily 
antivirus (ClamAV) scanner means an extensive I/O.

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