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    SubjectRe: [PATCH 1/4] nohz: Split extended quiescent state handling from nohz switch
    On Sun, Sep 04, 2011 at 02:01:30PM -0700, Paul E. McKenney wrote:
    > On Sat, Aug 20, 2011 at 07:30:49PM +0200, Frederic Weisbecker wrote:
    > > It is assumed that rcu won't be used once we switch to tickless
    > > mode and until we restart the tick. However this is not always
    > > true, as in x86-64 where we dereference the idle notifiers after
    > > the tick is stopped.
    > >
    > > To prepare for fixing this, split the tickless mode switching and
    > > RCU extended quiescent state logics.
    > > Make tick_nohz_stop/restart_sched_tick() RCU agnostic but provide
    > > a new pair of APIs tick_nohz_enter/exit_idle() that keep the
    > > old behaviour by handling both the nohz mode and RCU extended
    > > quiescent states, then convert every archs to use these.
    > >
    > > Archs that want to switch to RCU extended QS to some custom points
    > > can do it later by changing the parameter in tick_nohz_enter,exit_idle()
    > > to false and call rcu_enter,exit() separately.
    >
    > Hello, Frederic,
    >
    > Some of my testing indicates that it is necessary to push
    > tick_nohz_enter_idle() and tick_nohz_exit_idle() further down in the
    > powerpc case due to tracing that happens in functions called from
    > ppc_md.power_save(). My current guess is that for the pSeries flavor
    > of powerpc, these must be called from __trace_hcall_entry() and
    > __trace_hcall_exit(), probably controlled by a powerpc-specific per-CPU
    > variable.
    >
    > The following functions likely need help.
    >
    > cbe_power_save()
    > cpm_idle()
    > e500_idle()
    > idle_doze()
    > idle_spin()
    > ppc44x_idle()
    > ppc6xx_idle()
    > ps3_power_save()
    > pseries_dedicated_idle_sleep()
    > pseries_shared_idle_sleep()
    >
    > I am continuing testing. In the meantime, other thoughts?
    >
    > Thanx, Paul

    Yeah sure, I still have that in my todo list. I wanted to ensure
    first that at least you are fine with the new interface before I go
    fixing more detected bad callsites.

    Thanks.


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