Date: Fri, 5 Jan 2007 14:59:15 -0800 From: Luigi Rizzo <rizzo@icir.org> To: Paul Allen <nospam@nospam.com> Cc: freebsd-current@freebsd.org, lulf@stud.ntnu.no, Ivan Voras <ivoras@fer.hr>, freebsd-geom@freebsd.org Subject: Re: Pluggable Disk Schedulers in GEOM Message-ID: <20070105145915.B94175@xorpc.icir.org> In-Reply-To: <20070105212543.GA8574@heave.ugcs.caltech.edu>; from nospam@nospam.com on Fri, Jan 05, 2007 at 01:25:43PM -0800 References: <20070105123127.gnk0v58p44488g48@webmail.ntnu.no> <4085.1167997049@critter.freebsd.dk> <enlelj$63g$1@sea.gmane.org> <20070105184621.dh8kgoy7ko4gk4gc@webmail.ntnu.no> <20070105102905.A91349@xorpc.icir.org> <20070105212543.GA8574@heave.ugcs.caltech.edu>
index | next in thread | previous in thread | raw e-mail
On Fri, Jan 05, 2007 at 01:25:43PM -0800, Paul Allen wrote: > >From Luigi Rizzo <rizzo@icir.org>, Fri, Jan 05, 2007 at 10:29:05AM -0800: > > Essentially, a process doing e.g. a 'cvs checkout' on a large > > tree will still kill the performance of your disk no matter > > which scheduler you are using (elevator, hybrid, the dumb one that > > we wrote as an example). The reasons, i suspect, are a mixture > > of the ones described above. > > Interaction of the disk scheduler and softupdates? As I understand > the softupdate code, the disk scheduler would be ignorant of I/O that this was also on 4.11 which probably does not use softupdates. > depends on the completion of certain writes because issuing that I/O > to the lower layers is delayed until the equiv of bio_done occurs. > > I don't see what use a disk scheduler would be unless it is possible > to push information about any partial ordering requirements down to > the level at which the scheduler can see and enforce them. that does not mean that a scheduler is useless in general. in fact, what i find questionable is hardwiring unnecessary (in the sense that they are done only for performance reasons) ordering constraints in the layers above. I cannot comment for the disk, but e.g. for the process scheduler there are priority updates in many places depending on what the process is doing. cheers luigihome | help
Want to link to this message? Use this
URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20070105145915.B94175>