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    SubjectRe: [PATCH 3/3] rcu: Drive configuration directly from SMP and PREEMPT
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    On Sat, 2011-11-19 at 13:50 +0100, John Kacur wrote:
    > From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    >
    > This commit eliminates the possibility of running TREE_PREEMPT_RCU
    > when SMP=n and of running TINY_RCU when PREEMPT=y. People who really
    > want these combinations can hand-edit init/Kconfig, but eliminating
    > them as choices for production systems reduces the amount of testing
    > required. It will also allow cutting out a few #ifdefs.
    >
    > Note that running TREE_RCU and TINY_RCU on single-CPU systems using
    > SMP-built kernels is still supported.

    With this patch, I can see the need for the first patch (although
    there's things broken even for that), but is this really a stable fix?

    This looks more of an added feature than a bug fix. It's a bug fix if we
    consider running tree_rcu on UP a bug. Or better stated, will it break
    anything if we do that?

    -- Steve

    >
    > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    >
    > commit 8008e129dc90ff4f7a56cb033d6bd042afe3ed52 upstream
    > Cherry-picked for v3.0-rt and fixed-up merge conflicts
    > Note: This makes the depends lines for these options in init/Kconfig for v3.0-rt
    > match those for v3.2-rc2-rt3
    > Signed-off-by: John Kacur <jkacur@redhat.com>
    > ---
    > init/Kconfig | 6 +++---
    > 1 files changed, 3 insertions(+), 3 deletions(-)
    >
    > diff --git a/init/Kconfig b/init/Kconfig
    > index 89e40a4..5c1147e 100644
    > --- a/init/Kconfig
    > +++ b/init/Kconfig
    > @@ -391,7 +391,7 @@ config TREE_RCU
    >
    > config TREE_PREEMPT_RCU
    > bool "Preemptible tree-based hierarchical RCU"
    > - depends on PREEMPT
    > + depends on PREEMPT && SMP
    > help
    > This option selects the RCU implementation that is
    > designed for very large SMP systems with hundreds or
    > @@ -401,7 +401,7 @@ config TREE_PREEMPT_RCU
    >
    > config TINY_RCU
    > bool "UP-only small-memory-footprint RCU"
    > - depends on !SMP && !PREEMPT_RT_FULL
    > + depends on !PREEMPT && !SMP
    > help
    > This option selects the RCU implementation that is
    > designed for UP systems from which real-time response
    > @@ -410,7 +410,7 @@ config TINY_RCU
    >
    > config TINY_PREEMPT_RCU
    > bool "Preemptible UP-only small-memory-footprint RCU"
    > - depends on !SMP && PREEMPT && !PREEMPT_RT_FULL
    > + depends on PREEMPT && !SMP
    > help
    > This option selects the RCU implementation that is designed
    > for real-time UP systems. This option greatly reduces the




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