lkml.org 
[lkml]   [2011]   [Oct]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 2/2] blk-throttle: Take blkcg->lock while traversing blkcg->policy_list
    On 2011-10-21 14:10, Vivek Goyal wrote:
    > On Thu, Oct 20, 2011 at 02:29:58PM -0700, Tejun Heo wrote:
    >> Hello,
    >>
    >> On Thu, Oct 20, 2011 at 05:20:21PM -0400, Vivek Goyal wrote:
    >>> The only problem with this approach is that it will cleanup per device
    >>> weight rules also at elevator_exit() time which is not same as device
    >>> removal and one might device to bring CFQ back on device and we will
    >>> need the rules again.
    >>
    >> I actually think removoing those rules on elevator detach would be the
    >> right thing to do. We don't try to keep cfq setting across elevator
    >> switch. When we're switching from cfq, we're detaching iocg policy
    >> too. The settings going away is perfectly fine. I actually think
    >> it's a pretty bad idea to implement ad-hoc setting persistence in
    >> kernel. Just making sure that userland is notified is far better
    >> approach. Userland has all the facilities to deal with this type of
    >> situations.
    >>
    >> When switching from cfq to deadline, we lose the whole proportional io
    >> control. It's way more confusing to have lingering settings which
    >> don't do anything.
    >
    > I am not so sure about this. Suppose tomorrow another IO sheduler starts
    > taking into account the cgroup gloabl weight or cgroup per device weight
    > to do some kind of IO prioritization, then removing the rules upon
    > changing the IO schduler will not make sense.
    >
    > IOW, rules are per cgroup per device and not per cgroup per IO scheduler
    > and more than one IO scheduler should be able to share the rules.

    FWIW, I agree with Tejun here. A switch operation is a reset, start from
    scratch. We don't preserve other per IO-scheduler settings on a switch,
    preserving _some_ settings is just confusing.

    --
    Jens Axboe



    \
     
     \ /
      Last update: 2011-10-25 16:35    [W:3.798 / U:0.436 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site