On Sat, Mar 31, 2012 at 11:32:00PM +0100, Russell King - ARM Linux wrote: > On Sun, Apr 01, 2012 at 12:33:21AM +0800, Paul E. McKenney wrote: > > Although there have been numerous complaints about the complexity of > > parallel programming (especially over the past 5-10 years), the plain > > truth is that the incremental complexity of parallel programming over > > that of sequential programming is not as large as is commonly believed. > > Despite that you might have heard, the mind-numbing complexity of modern > > computer systems is not due so much to there being multiple CPUs, but > > rather to there being any CPUs at all. In short, for the ultimate in > > computer-system simplicity, the optimal choice is NR_CPUS=0. > > > > This commit therefore limits kernel builds to zero CPUs. This change > > has the beneficial side effect of rendering all kernel bugs harmless. > > Furthermore, this commit enables additional beneficial changes, for > > example, the removal of those parts of the kernel that are not needed > > when there are zero CPUs. > > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > > Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > Great work, but I don't think you've gone far enough with this. > > What would really help is if you could consolidate all these NR_CPUS > definitions into one place so we don't have essentially the same thing > scattered across all these architectures. We're already doing this on > ARM across our platforms, and its about time such an approach was taken > across the entire kernel tree. > > It looks like the MIPS solution would be the best one to pick. > Could you rework your patch to do this please? > > While you're at it, you might like to consider that having zero CPUs > makes all this architecture support redundant, so maybe you've missed > a trick there - according to my count, we could get rid of almost 3 > million lines of code from arch. We could replace all that with a > single standard implementation. > > Bah, maybe I shouldn't have pushed that bpf_jit code for ARM after all... ;-) ;-) ;-) Thanx, Paul
