On Mon, Nov 21, 2011 at 5:10 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Sat, 2011-11-19 at 13:50 +0100, John Kacur wrote: >> From: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> >> >> 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@xxxxxxxxxxxxxxxxxx> >> >> 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@xxxxxxxxxx> >> --- >> 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 > Imagine you have a uni-processor system and want to do real-time. According to the descriptions in init/Kconfig, you would want to select TINY_PREEMPT_RCU. The description is This option selects the RCU implementation that is designed for real-time UP systems. This option greatly reduces the memory footprint of RCU. Without this patch, you cannot choose this option because of the && !PREEMPT_RT_FULL So, that is a bug, and makes this patch appropriate for stable. I suppose if you want to be really conservative, you can say we only need that third hunk. However, this upstream patch, makes these options in v3.0-rt match the options in v3.2-rc2-rt3. Furthermore, it doesn't seem like a good idea to me to support configurations in a stable branch that are not supported upstream. Thanks John -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
