Date: Tue, 09 Feb 2010 15:37:03 +1100 From: Michael Vince <mv@thebeastie.org> To: Jordi Espasa Clofent <jespasac@minibofh.org> Cc: freebsd-stable@freebsd.org Subject: Re: ionice in FreeBSD? Message-ID: <4B70E66F.2040203@thebeastie.org> In-Reply-To: <4B696360.3070209@minibofh.org> References: <4B685EBA.4020501@minibofh.org> <4B695A1A.1000505@incunabulum.net> <4B696360.3070209@minibofh.org>
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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
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