Messages in this thread | | | Date | Mon, 7 Jan 2013 14:19:15 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 1/1] Tiny RCU changes for 3.9 |
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On Mon, Jan 07, 2013 at 09:56:06AM -0800, Josh Triplett wrote: > On Mon, Jan 07, 2013 at 08:57:48AM -0800, Paul E. McKenney wrote: > > 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 <tglx@linutronix.de> > > > > Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> > > > > Signed-off-by: Paul E. McKenney <paulmck@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. ;-) > > Just don't pass --cover-letter to git format-patch and you won't get the > 0/1.
Ah, good point! Thank you!
> > > 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? > > I understand the rationale; I just think it would become clearer if you > added an internal-only Kconfig symbol selected in both cases and change > the conditionals to use that.
My concern was that this would confuse people into thinking that the code under those #ifdefs was all the stall-warning code that there was.
I suppose this could be forestalled with a suitably clever name... CONFIG_RCU_CPU_STALL_TINY_TOO? Better names?
Thanx, Paul
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