On Thu 21-12-17 18:31:19, kemi wrote: > > > On 2017年12月21日 16:59, Michal Hocko wrote: > > On Thu 21-12-17 16:23:23, kemi wrote: > >> > >> > >> On 2017年12月21日 16:17, Michal Hocko wrote: > > [...] > >>> Can you see any difference with a more generic workload? > >>> > >> > >> I didn't see obvious improvement for will-it-scale.page_fault1 > >> Two reasons for that: > >> 1) too long code path > >> 2) server zone lock and lru lock contention (access to buddy system > >> frequently) > > > > OK. So does the patch helps for anything other than a microbenchmark? > > > >>>> Some thinking about that: > >>>> a) the overhead due to cache bouncing caused by NUMA counter update in > >>>> fast path > >>>> severely increase with more and more CPUs cores > >>> > >>> What is an effect on a smaller system with fewer CPUs? > >>> > >> > >> Several CPU cycles can be saved using single thread for that. > >> > >>>> b) AFAIK, the typical usage scenario (similar at least)for which this > >>>> optimization can > >>>> benefit is 10/40G NIC used in high-speed data center network of cloud > >>>> service providers. > >>> > >>> I would expect those would disable the numa accounting altogether. > >>> > >> > >> Yes, but it is still worthy to do some optimization, isn't? > > > > Ohh, I am not opposing optimizations but you should make sure that they > > are worth the additional code and special casing. As I've said I am not > > convinced special casing numa counters is good. You can play with the > > threshold scaling for larger CPU count but let's make sure that the > > benefit is really measurable for normal workloads. Special ones will > > disable the numa accounting anyway. > > > > I understood. Could you give me some suggestion for those normal workloads, > Thanks. > I will have a try and post the data ASAP.
Well, to be honest, I am really confused what is your objective for these optimizations then. I hope we have agreed that workloads which really need to squeeze every single CPU cycle in the allocation path will simply disable the whole numa stat thing. I haven't yet heard about any use case which would really required numa stats and suffer from the numa stats overhead. I can see some arguments for a better threshold scaling but that requires to check wider range of tests to show there are no unintended changes. I am not really confident you understand that when you are asking for "those normal workloads". So please, try to step back, rethink who you are optimizing for and act accordingly. If I were you I would repost the first patch which only integrates numa stats because that removes a lot of pointless code and that is a win of its own. -- Michal Hocko SUSE Labs
