On Mon, Jan 07, 2013 at 07:58:10AM -0800, Josh Triplett wrote:
> On Sat, Jan 05, 2013 at 09:50:59AM -0800, Paul E. McKenney wrote:
> > rcu: Provide RCU CPU stall warnings for tiny RCU
> >
> > Tiny RCU has historically omitted RCU CPU stall warnings in order to
> > reduce memory requirements, however, lack of these warnings caused Thomas
> > Gleixner some debugging pain recently. Therefore, this commit adds RCU
> > CPU stall warnings to tiny RCU if RCU_TRACE=y. This keeps the memory
> > footprint small, while still enabling CPU stall warnings in kernels
> > built to enable them.
> >
> > This is still a bit on the high-risk side, so running this will likely
> > be a debugging exercise.
> >
> > Reported-by: Thomas Gleixner <t...@linutronix.de>
> > Signed-off-by: Paul E. McKenney <paul.mcken...@linaro.org>
> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
>
> Did you generate this patch with something other than git? The
> formatting seems a bit off: it doesn't have a diffstat or the usual
> "---" line between the commit message and the patch.
Indeed I did -- couldn't see the point of sending a 0/1 and 1/1
series of patches. ;-)
> This patch seems reasonable to me, but the repeated use of #if
> defined(CONFIG_SMP) || defined(CONFIG_RCU_TRACE) seems somewhat
> annoying, and fragile if you ever decide to change the conditions. How
> about defining an appropriate symbol in Kconfig for stall warnings, and
> using that?
But I only just removed the config option for SMP RCU stall warnings. ;-)
But I must agree that "defined(CONFIG_SMP) || defined(CONFIG_RCU_TRACE)"
is a bit obscure. The rationale is that RCU stall warnings are
unconditionally enabled in SMP kernels, but don't want to be in
TINY_RCU kernels due to size constraints. I therefore put it under
CONFIG_RCU_TRACE, which also contains other TINY_RCU debugging-style
options. Would adding a comment to this effect help?
Thanx, Paul
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