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.
--
I must not fear. Fear is the mind-killer. Fear is the little-death that
brings total obliteration. I will face my fear. I will permit it to pass
over me and through me. And when it has gone past I will turn the inner
eye to see its path. Where the fear has gone there will be nothing. Only
I will remain.
Bene Gesserit Litany Against Fear.
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