[lkml]   [2011]   [May]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [tip:core/rcu] Revert "rcu: Decrease memory-barrier usage based on semi-formal proof"
    On 05/24/2011 02:23 PM, Yinghai Lu wrote:
    > On 05/23/2011 06:35 PM, Paul E. McKenney wrote:
    >> On Mon, May 23, 2011 at 06:26:23PM -0700, Yinghai Lu wrote:
    >>> On 05/23/2011 06:18 PM, Paul E. McKenney wrote:
    >>>> OK, so it looks like I need to get this out of the way in order to track
    >>>> down the delays. Or does reverting PeterZ's patch get you a stable
    >>>> system, but with the longish delays in memory_dev_init()? If the latter,
    >>>> it might be more productive to handle the two problems separately.
    >>>> For whatever it is worth, I do see about 5% increase in grace-period
    >>>> duration when switching to kthreads. This is acceptable -- your
    >>>> 30x increase clearly is completely unacceptable and must be fixed.
    >>>> Other than that, the main thing that affects grace period duration is
    >>>> the setting of CONFIG_HZ -- the smaller the HZ value, the longer the
    >>>> grace-period duration.
    >>> for my 1024g system when memory hotadd is enabled in kernel config:
    >>> 1. current linus tree + tip tree: memory_dev_init will take about 100s.
    >>> 2. current linus tree + tip tree + your tree - Peterz patch:
    >>> a. on fedora 14 gcc: will cost about 4s: like old times
    >>> b. on opensuse 11.3 gcc: will cost about 10s.
    >> So some patch in my tree that is not yet in tip makes things better?
    >> If so, could you please see which one? Maybe that would give me a hint
    >> that could make things better on opensuse 11.3 as well.
    > today's tip:
    > [ 31.795597] cpu_dev_init done
    > [ 40.930202] memory_dev_init done

    another boot from tip got:

    [ 35.211927] cpu_dev_init done
    [ 136.053698] memory_dev_init done

    wonder if you can have clean revert for

    commit a26ac2455ffcf3be5c6ef92bc6df7182700f2114
    > Author: Paul E. McKenney <>
    > Date: Wed Jan 12 14:10:23 2011 -0800
    > rcu: move TREE_RCU from softirq to kthread
    > If RCU priority boosting is to be meaningful, callback invocation must
    > be boosted in addition to preempted RCU readers. Otherwise, in presence
    > of CPU real-time threads, the grace period ends, but the callbacks don't
    > get invoked. If the callbacks don't get invoked, the associated memory
    > doesn't get freed, so the system is still subject to OOM.
    > But it is not reasonable to priority-boost RCU_SOFTIRQ, so this commit
    > moves the callback invocations to a kthread, which can be boosted easily.
    > Also add comments and properly synchronized all accesses to
    > rcu_cpu_kthread_task, as suggested by Lai Jiangshan.
    > Signed-off-by: Paul E. McKenney <>
    > Signed-off-by: Paul E. McKenney <>
    > Reviewed-by: Josh Triplett <>


    Yinghai Lu

     \ /
      Last update: 2011-05-25 02:13    [W:0.026 / U:11.696 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site