Date: Wed, 15 Sep 2010 18:00:33 +0200 From: Andre Oppermann <andre@freebsd.org> To: Andriy Gapon <avg@freebsd.org> Cc: freebsd-fs@freebsd.org, jhell <jhell@DataIX.net>, Steven Hartland <killing@multiplay.co.uk>, Pawel Jakub Dawidek <pjd@freebsd.org>, freebsd-net@freebsd.org Subject: Re: zfs very poor performance compared to ufs due to lack of cache? Message-ID: <4C90EDA1.6020501@freebsd.org> In-Reply-To: <4C90E869.8000400@freebsd.org> References: <5DB6E7C798E44D33A05673F4B773405E@multiplay.co.uk><AANLkTikNhsj5myhQCoPaNytUbpHtox1vg9AZm1N-OcMO@mail.gmail.com><4C85E91E.1010602@icyb.net.ua><4C873914.40404@freebsd.org><20100908084855.GF2465@deviant.kiev.zoral.com.ua><4C874F00.3050605@freebsd.org><A6D7E134B24F42E395C30A375A6B50AF@multiplay.co.uk><4C8D087B.5040404@freebsd.org><03537796FAB54E02959E2D64FC83004F@multiplay.co.uk><4C8D280F.3040803@freebsd.org><3FBF66BF11AA4CBBA6124CA435A4A31B@multiplay.co.uk><4C8E4212.30000@freebsd.org> <B98EBECBD399417CA5390C20627384B1@multiplay.co.uk> <D79F15FEB5794315BD8668E40B414BF0@multiplay.co.uk> <4C90B4C8.90203@freebsd.org> <6DFACB27CA8A4A22898BC81E55C4FD36@multiplay.co.uk> <4C90D3A1.7030008@freebsd.org> <0B1A90A08DFE4ADA9540F9F3846FDF38@multiplay.co.uk> <4C90E328.20606@freebsd.org> <4C90E869.8000400@freebsd.org>
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On 15.09.2010 17:38, Andriy Gapon wrote: > on 15/09/2010 18:15 Andriy Gapon said the following: >> on 15/09/2010 18:04 Steven Hartland said the following: >>> Hmm, so taking a different track on the issue is the a way to make sendfile use data >>> directly from ARC instead of having to copy it first? >> >> Well, theoretically everything is possible, but I am not sure if it's feasible. >> It's a lot of work anyways, it should be a very specialized sendfile and a lot if >> inter-layer knowledge and dependencies. >> Don't hold your breath for it. > > Perhaps some middle-ground solution can be developed with less effort. > This solution would be specific to filesystems that don't use buffer cache, so it > wouldn't touch any pages, but instead it would use regular VOP_READ into a mbuf. > So, there would be copying, but page caches won't be unnecessarily "polluted" with > second copy of the data and this all would happen in kernel giving an advantage > over userland solution with read(2)+send(2). Is there a quick way of deciding within sendfile(2) whether a file resides on a filesystem that doesn't use the buffer cache? > Having said that, I see that OpenSolaris has a mechanism for something like that. > The mechanism can either globally enabled or enabled for file over certain size. > The mechanism uses dedicated kernel threads that get data using direct I/O, buffer > and send it. > That's my impression from a quick look, I may have gotten things wrong. -- Andre
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