lkml.org 
[lkml]   [2012]   [Jan]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 08/17] blkcg: shoot down blkio_groups on elevator switch
    On Mon, 23.01.12 10:43, Tejun Heo (tj@kernel.org) wrote:

    >
    > On Mon, Jan 23, 2012 at 01:27:45PM -0500, Vivek Goyal wrote:
    > > > Why can't systemd order elevator switch before other actions?
    > >
    > > Because systemd does not know. For systemd it is just launching services
    > > and what services are doing is not known to systemd.
    > >
    > > I think systemd does have some facilities so that services can express
    > > dependency on other services and dependent service blocks on completion
    > > of service it is depenent on. So may be in this case any service dealing
    > > with cgroups shall have to be dependent on this service which tunes
    > > the system and changes elevator.
    >
    > I'm sure systemd has enough facility for expressing this dependency.
    > Where this configuration belongs to is a different question tho. I
    > don't know how the tuned thing works but configurations like this are
    > bound to devices and should be part of device discovery / hotplug
    > sequence. IOW, it should be something which ultimately runs off udev
    > events as part of device found event.

    I didn't really follow the whole discussion here, but if this is about
    adjusting parameters of a block device as the block device shows up this
    must necessarily happen in an udev rule (and not in a daemon watching
    block devices using libudev), since you most likely need the
    synchronicity: i.e. you want to avoid that normal (libudev-using)
    userspace code ever sees the device before those params are written to
    the device. A daemon asynchronously watching the devices with libudev
    for adjusting such tunables is necessarily racy.

    Lennart

    --
    Lennart Poettering - Red Hat, Inc.


    \
     
     \ /
      Last update: 2012-01-23 21:47    [W:0.035 / U:0.444 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site