On 01/23/2015 12:14 AM, WANG Chao wrote: > On 01/22/15 at 11:22am, Rik van Riel wrote: >> > On 01/22/2015 11:19 AM, Davidlohr Bueso wrote: >>> > > On Thu, 2015-01-22 at 15:57 +0800, WANG Chao wrote: >>>> > >> Hi, Davidlohr >>>> > >> >>>> > >> On 01/21/15 at 11:46pm, Davidlohr Bueso wrote: >>>>> > >>> On Thu, 2015-01-22 at 14:29 +0800, WANG Chao wrote: >>>>>> > >>>> Add a new kconfig option VMACACHE_SHIFT (as a power of 2) to specify the >>>>>> > >>>> number of slots vma cache has for each thread. Range is chosen 0-4 (1-16 >>>>>> > >>>> slots) to consider both overhead and performance penalty. Default is 2 >>>>>> > >>>> (4 slots) as it originally is, which provides good enough balance. >>>>>> > >>>> >>>>> > >>> >>>>> > >>> Nack. I don't feel comfortable making scalability features of core code >>>>> > >>> configurable. >>>> > >> >>>> > >> Out of respect, is this a general rule not making scalability features >>>> > >> of core code configurable? >>> > > >>> > > I doubt its a rule, just common sense. Users have no business >>> > > configuring such low level details. The optimizations need to >>> > > transparently work for everyone. >> > >> > There may sometimes be a good reason for making this kind of >> > thing configurable, but since there were no performance >> > numbers in the changelog, I have not seen any such reason for >> > this particular change :) > True. I didn't run any kind of benchmark, thus no numbers here. This is > purely hypothetical. > > I'm glad to run some tests. For the sake of consistency, could you > please show me a hint how do you measure at the first place? I can do > hit-rate, but I don't know how you measure cpu cycles. Could you > elaborate? I don't think there's a need to look for problems where there are none. Have you observed a performance issue that might be improved by changing the shift here? Thanks, Sasha -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>