lkml.org 
[lkml]   [2010]   [Mar]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 2/4] stop_machine: reimplement using cpuhog
    On Tue, Mar 09, 2010 at 12:53:21AM +0900, Tejun Heo wrote:
    > Reimplement stop_machine using cpuhog. As cpuhogs are guaranteed to
    > be available for all online cpus, stop_machine_create/destroy() are no
    > longer necessary and removed.
    >
    > With resource management and synchronization handled by cpuhog, the
    > new implementation is much simpler. Asking the cpuhog to execute the
    > stop_cpu() state machine on all online cpus with cpu hotplug disabled
    > is enough.
    >
    > stop_machine itself doesn't need to manage any global resources
    > anymore, so all per-instance information is rolled into struct
    > stop_machine_data and the mutex and all static data variables are
    > removed.
    >
    > The previous implementation created and destroyed RT workqueues as
    > necessary which made stop_machine() calls highly expensive on very
    > large machines. According to Dimitri Sivanich, preventing the dynamic
    > creation/destruction makes booting faster more than twice on very
    > large machines. cpuhog resources are preallocated for all online cpus
    > and should have the same effect.
    >
    > Signed-off-by: Tejun Heo <tj@kernel.org>
    > Cc: Rusty Russell <rusty@rustcorp.com.au>
    > Cc: Oleg Nesterov <oleg@redhat.com>
    > Cc: Dimitri Sivanich <sivanich@sgi.com>
    > ---
    > arch/s390/kernel/time.c | 1 -
    > drivers/xen/manage.c | 14 +---
    > include/linux/stop_machine.h | 20 -----
    > kernel/cpu.c | 8 --
    > kernel/module.c | 14 +---
    > kernel/stop_machine.c | 162 ++++++++++--------------------------------
    > 6 files changed, 42 insertions(+), 177 deletions(-)
    >
    > diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
    > index 65065ac..afe429e 100644
    > --- a/arch/s390/kernel/time.c
    > +++ b/arch/s390/kernel/time.c
    > @@ -397,7 +397,6 @@ static void __init time_init_wq(void)
    > if (time_sync_wq)
    > return;
    > time_sync_wq = create_singlethread_workqueue("timesync");
    > - stop_machine_create();
    > }
    >
    > /*

    The reason we introduced stop_machine_create/destroy was to have a non-failing
    variant that doesn't rely on I/O.
    If we ever see a timesync machine check no I/O will succeed (it blocks) until
    clocks have been synchronized. That means also that we rely on the non-blocking
    semantics that those functions must have that are called via stop_machine.
    This isn't true anymore with the cpu hog infrastructure:
    if passed a blocking function that could wait on I/O we won't see any progress
    anymore and the machine is dead.


    \
     
     \ /
      Last update: 2010-03-08 18:13    [from the cache]
    ©2003-2014 Jasper Spaans. hosted at Digital Ocean