ionice in FreeBSD?

[Michael Vince]

On 3/02/2010 10:52 PM, Jordi Espasa Clofent wrote:
> 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.
>
Programs like Rsync do provide --bwlimit= which work great in slowing it 
down to a desired level.

I can't help but think every program that can use too much IO should 
have it's own IO/speed switch of some sort.
I can only hope that in general nix evolution that all programs that can 
over use IO will offer a switch to slow it down like Rsync does.

Using a while ionice can be a useful feature it can also be said that 
there are too many instances where it's being used as a hack to deal 
with a program that isn't offering all the functionality that it should.

Cheers,
Mike