On Tue, 28 Nov 2017 10:40:52 -0800 Andi Kleen <a...@linux.intel.com> wrote:
> Vlastimil Babka <vba...@suse.cz> writes: > > > > I'm worried about the "for_each_possible..." approach here and elsewhere > > in the patch as it can be rather excessive compared to the online number > > of cpus (we've seen BIOSes report large numbers of possible CPU's). IIRC > > Even if they report a few hundred extra reading some more shared cache lines > is very cheap. The prefetcher usually quickly figures out such a pattern > and reads it all in parallel. > > I doubt it will be noticeable, especially not in a slow path > like reading something from proc/sys. We say that, then a few years it comes back and bites us on our trailing edges. > > the general approach with vmstat is to query just online cpu's / nodes, > > and if they go offline, transfer their accumulated stats to some other > > "victim"? > > That's very complicated, and unlikely to be worth it. for_each_online_cpu() and a few-line hotplug handler? I'd like to see an implementation before deciding that it's too complex...
