Re: [RFC 0/5] rcu: Introduce leaf_node_for_each_mask_possible_cpu() and its friend

From: Boqun Feng
Date: Fri Dec 09 2016 - 19:46:11 EST

On Fri, Dec 09, 2016 at 03:49:45PM -0800, Paul E. McKenney wrote:
> On Fri, Dec 09, 2016 at 04:48:22PM +0800, Boqun Feng wrote:
> > Hi Paul,
> >
> > While reading the discussion at:
> >
> >
> This discussion was for stalls specifically, rather than for routine
> scans of the bitmasks.
> But it does look to save some code, so worth looking into.
> > I figured we might use this fact to save some extra checks in RCU core code,
> > currently we iterate over all the possible CPUs on a leaf node, check whether
> > they were masked in a certain mask and do something. However, given the fact
> > that the masks on a leaf node should always be sparse than the corresponding
> > part of cpu_possible_mask, we'd better iterate over all bits in a mask and
> > check whether the corresponding CPU is possible or not.
> >
> > So I made this RFC, I did a simple build/boot/rcutorture test on my box with
> > SMP=4, nothing bad happens. Currently I'm waiting for the 0day and trying to
> > test this one a bigger system, in the meanwhile, looking forwards to any
> > comment and suggestion.
> >
> > So thoughts?
> By analogy with for_each_cpu() and for_each_possible_cpu(), the name
> should instead be for_each_leaf_node_cpu(), the tradition of excessively
> long names in RCU notwithstanding. ;-)

Make sense ;-)

I think it's more appropriate to call it for_each_leaf_node_mask_cpu(),
because we don't iterate all cpus of a leaf node. The word "possible"
could be dropped because obviously we won't iterate over "impossible"
cpus in a leaf node ;-)

Will modify that in next version.


> Thanx, Paul

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