On Fri, Sep 06, 2013 at 10:08:22AM +0200, Geert Uytterhoeven wrote: > On Tue, Aug 20, 2013 at 4:47 AM, Paul E. McKenney > <paulmck@xxxxxxxxxxxxxxxxxx> wrote: > > --- a/kernel/time/Kconfig > > +++ b/kernel/time/Kconfig > > @@ -157,6 +157,33 @@ config NO_HZ_FULL_SYSIDLE > > > > Say N if you are unsure. > > > > +config NO_HZ_FULL_SYSIDLE_SMALL > > + int "Number of CPUs above which large-system approach is used" > > + depends on NO_HZ_FULL_SYSIDLE > > + range 1 NR_CPUS > > This causes "kernel/time/Kconfig:162:warning: range is invalid" on m68k and > all other architectures that do not support SMP. > > How to reproduce: > make ARCH=m68k defconfig OK, this does complain, but seems to give a reasonable .config file. (From what I can tell.) It would clearly be good to get rid of the complaint. > Furthermore, it seems only hexagon, metag, mips, and x86 set NR_CPUS to 1 > if !SMP. On other architectures, NR_CPUS is not defined and presumed to be 0. Would it make sense to require that NR_CPUS=1 for !SMP? > Hence in non-interactive configs (e.g. "make defconfig"), > NO_HZ_FULL_SYSIDLE_SMALL will end up as 0. > In interactive configs (e.g. "make oldconfig") Kconfig suggest "0" as > the default, > but refuses to accept it as it doesn't fall within the range 1..0. > > How to reproduce: > Remove the "depends on NO_HZ_FULL_SYSIDLE" > make ARCH=powerpc mpc83xx_defconfig > grep NO_HZ_FULL_SYSIDLE_SMALL .config > -> CONFIG_NO_HZ_FULL_SYSIDLE_SMALL=0 > sed 's/CONFIG_NO_HZ_FULL_SYSIDLE_SMALL=0//g' -i .config > make ARCH=powerpc oldconfig > -> no value is accepted If it turns out that there is some reason by NR_CPUS=1 is impossible, there are a few things that I could do: I could just leave the range off, which would allow people to give nonsense values. This would be harmless in the code, for example, a negative value would simply disable small-system handling, while a too-large value would similarly disable large-system handling. Might be a bit obnoxious for the guy who typoed and then wasted a kernel build/boot/test cycle, but it is an option. I could use a small fixed range (say from 1 to 64), which would provide at least some checking. In the unlikely event that someone really wants more than 64 CPUs handled with small-system handling, we could revisit at that point. I tried creating a NR_CPUS_REALLY as follows: config NR_CPUS_REALLY int "Fixed version of NR_CPUS" default NR_CPUS if NR_CPUS default 1 if !NR_CPUS But this still gave a warning on the first "default" even though it was not in effect. I also tried using Kconfig "if": if SMP config NR_CPUS_REALLY int "Fixed version of NR_CPUS" default NR_CPUS endif if !SMP config NR_CPUS_REALLY int "Fixed version of NR_CPUS" default 1 if !SMP endif However, Kconfig complained about the use of NR_CPUS even though this was under an "if" whose condition was not set. Perhaps someone with better Kconfig-fu than I have can come up with something. Defining NR_CPUS=1 if !SMP is looking pretty good to me just now. This would probably have other benefits -- I cannot be the only person who ever wanted this. ;-) Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
