On 09/09/2015 03:40 PM, Austin S Hemmelgarn wrote: > On 2015-09-09 08:12, Boaz Harrosh wrote: >> On 09/09/2015 02:28 PM, Austin S Hemmelgarn wrote: >>> On 2015-09-08 16:00, Elliott, Robert (Persistent Memory) wrote: >> <> >> >>> this may actually make things slower (the particular effect of SSD mode >>> is that it tries to spread allocations out as much as possible, as this >>> helps with wear-leveling on many SSD's). >>> >> >> For DRAM based NvDIMM it matters not at all. For Flash based or the new >> 3d Xpoint it is a plus, so no harm in leaving it in >> > Looking at it from another perspective however, a lot of modern RAM > modules will stripe the bits across multiple chips to improve > performance. In such a situation, BTRFS making the effort to spread out > the allocation as much as possible may have an impact because that > allocation path is slower than the regular one (not by much, but even a > few microseconds can make a difference when it is getting called a lot). > > It is pointless to argue about this, but the allocations are 4k aligned any which way, which means you are right at the beginning of the striping, the RAM striping is a cacheline (64 bytes) granularity. I think you will never find a single micro benchmark that will ever produce a difference. Cheers Boaz -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
