Date: Tue, 29 May 2012 23:12:47 +0200 From: Kees Jan Koster <kjkoster@gmail.com> To: Freddie Cash <fjwcash@gmail.com> Cc: freebsd-stable@freebsd.org Subject: Re: FreeBSD 9.0 hangs on heavy I/O Message-ID: <17320979-2ED2-4DF2-97E9-09035F4DD3BB@gmail.com> In-Reply-To: <CAOjFWZ7964oeTNZqADj4cRt3kkdOf5Mwyx8GQDnJnZ8vyONckg@mail.gmail.com> References: <BD5D6BB6-8CFF-456A-B03E-05454EB03AB6@gmail.com> <CAOjFWZ40LX%2B8Lw15mHDG8F3nN0aex5EpqVdjPxRPS89t1Fqkiw@mail.gmail.com> <CAOjFWZ7964oeTNZqADj4cRt3kkdOf5Mwyx8GQDnJnZ8vyONckg@mail.gmail.com>
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Dear Freddie, >> You may want to play around with gshed, the GEOM Scheduler. >>=20 >> Matt Dillon did a bunch of tests comparing FreeBSD+UFS to >> DragonflyBSD+HAMMER and found that FreeBSD starves read threads in >> order to satisfy write threads (or the other way around?). But, >> adding gsched into the mix helped things immensely, allowing mixed >> reads/writes to better shares disk I/O resources. >>=20 >> I'll see if I can dig up a link to his testing e-mail messages. >=20 > Here's the post, part of a thread on benchmarking RAID controllers: >=20 > http://leaf.dragonflybsd.org/mailarchive/kernel/2011-07/msg00034.html I looked at "sysctl kern.geom.confdot" (another ridiculously useful = feature) to see where the scheduler should be placed. The way I was thinking, I should place a scheduler in such a way that = writes to one physical device (ada3 in my case) do not cause reads on = another device to stall (e.g. ada2, where the database lives). However, = it looks like the GEOM tree is actually a GEOM bush, with a separate = tree for each device. Am I missing something? Is there a way to schedule across devices? Is = the bush a tree after all, maybe? -- Kees Jan http://java-monitor.com/ kjkoster@kjkoster.org +31651838192 The secret of success lies in the stability of the goal. -- Benjamin = Disraeli
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