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Date: Wed, 03 Feb 2010 11:12:26 +0000
From: Bruce Simpson <bms@incunabulum.net>
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Subject: Re: ionice in FreeBSD?
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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.

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' ?