Date: Wed, 03 Feb 2010 11:12:26 +0000 From: Bruce Simpson <bms@incunabulum.net> To: freebsd-stable@freebsd.org Subject: Re: ionice in FreeBSD? Message-ID: <4B695A1A.1000505@incunabulum.net> In-Reply-To: <4B685EBA.4020501@minibofh.org> References: <4B685EBA.4020501@minibofh.org>
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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' ?
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