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>
next in thread | previous in thread | raw e-mail | index | archive | help
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 luigi
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20070105145915.B94175>