On Thu, Dec 15, 2016 at 03:10:15PM +0000, Mark Rutland wrote: > On Thu, Dec 15, 2016 at 10:38:58PM +0800, Boqun Feng wrote: > > On Thu, Dec 15, 2016 at 11:43:52AM +0000, Mark Rutland wrote: > > > On Thu, Dec 15, 2016 at 10:42:00AM +0800, Boqun Feng wrote: > > > > +#define MASK_BITS(mask) (BITS_PER_BYTE * sizeof(mask)) > > > > +/* > > > > + * Iterate over all CPUs a leaf RCU node which are still masked in > > > > + * @mask. > > > > + * > > > > + * Note @rnp has to be a leaf node and @mask has to belong to @rnp. > > > > > > Not a big deal, but perhaps it's worth enforcing this? If we took just > > > the name of the mask here, (e.g. qsmask rather than rnp->qsmask), we > > > could have the macro always use (rnp)->(mask). That would also make the > > > invocations shorter. > > > > I thought about this approach, but there may be some cases it seems > > inappropriate, see patch #5, passing "qsmaskinitnext" directly to the > > for_each_leaf_node_cpu() might be OK, but it just break another > > abstraction layer which rcu_rnp_online_cpus() provides. > > I had missed that. Given that, not enforcingi t makes sense to me. > > > > > And we > > > > + * assume that no CPU is masked in @mask but not set in > > > > cpu_possible_mask. IOW, > > > > + * masks of a leaf node never set a bit for an "impossible" CPU. > > > > + */ > > > > +#define for_each_leaf_node_cpu(rnp, mask, cpu) \ > > > > + for ((cpu) = (rnp)->grplo + find_first_bit(&(mask), > > > > MASK_BITS(mask)); \ > > > > + (cpu) <= (rnp)->grphi && > > > > !WARN_ON_ONCE(!cpu_possible(cpu)); \ > > > > > > If this happens, we'll exit the loop. If there are any reamining > > > possible CPUs, we'll skip them, which would be less than ideal. > > > > > > I guess this shouldn't happen anyway, but it might be worth continuing. > > > > > > > I chose to break if we met impossible only because I wanted to avoid > > using that "if(...) else" trick in an iteration macro ;-) > > Understandable. ;) > > > I don't know whether this is the first time something like this is > > brought into kernel, so I'm kinda hesitating to bring this in. But seems > > I got you as one supporter ;-) > > > > Certainly, skip is better than stop. > > From a quick look around, I found at least a few instances of the pattern. > e.g. > > include/linux/cpufreq.h: > > #define cpufreq_for_each_valid_entry(pos, table) \ > for (pos = table; pos->frequency != CPUFREQ_TABLE_END; pos++) \ > if (pos->frequency == CPUFREQ_ENTRY_INVALID) \ > continue; \ > else > > tools/perf/util/build-id.c: > #define dsos__for_each_with_build_id(pos, head) \ > list_for_each_entry(pos, head, node) \ > if (!pos->has_build_id) \ > continue; \ > else > > Some drivers, like drivers/net/ethernet/broadcom/bnx2x/bnx2x.h really love it! >
Thank you! So no reason we don't use it, let me send an updated patch ;-) Regards, Boqun > Thanks, > Mark.
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