Date: Wed, 03 Feb 2010 12:52:00 +0100 From: Jordi Espasa Clofent <jespasac@minibofh.org> To: freebsd-stable@freebsd.org Subject: Re: ionice in FreeBSD? Message-ID: <4B696360.3070209@minibofh.org> In-Reply-To: <4B695A1A.1000505@incunabulum.net> References: <4B685EBA.4020501@minibofh.org> <4B695A1A.1000505@incunabulum.net>
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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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