On 12/10/18 6:24 AM, 臧琳 wrote: > My observation is that when “jmap histo” iterating objects , the > object’s klass > is identified and then hash idx in KlassInfoTable’s buckets[] is > calculated by mod > of _num_bucktes, which would issue a heavy instruction idiv on x86 platform. > It > means for every object scanned, a idiv instruction is issued, which lag the > performance espically when > there are large number of objects in heap.
I'm surprised that GCC uses idiv in this case: it has an optimization for constant modulo which doesn't use division. There is sometimes an advantage for using hash tables of prime size. Is it that the size of the table is not a constant that GCC can see? -- Andrew Haley Java Platform Lead Engineer Red Hat UK Ltd. <https://www.redhat.com> EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671
