_fixnum slow? (despite docs)

Questions & Answers
6

In the interest of more broadly testing the FFI change, I've pushed the revised FFI implementation for Racket, letting Racket's copy of Chez Scheme temporarily diverge from the main Chez Scheme branch while a PR is considered there.

Here are some rough performance results. The "fix" column shows peformance after repairing a broken check in v8.15 that disabled an intended fast path. The "new" column shows the latest Racket with the revised FFI implementation. The "ref-stress-test" group of results correspond to the original post, but using in-range. The last four examples are about foreign call as much as (or instead of) ptr-ref and ptr-set!. For example, "math.rkt" uses bf+, which is relevant because it uses MPFR and GMP bindings. Programs here.

CPU time in milliseconds
                  v8.15     fix     new
ref-stress-test
  vector   ref      11      11       11
  _ulong   ref      37      38   >>  17
  _ulong   set!    631  >>  72   >>  18
  _int     ref      37      37   >>  16
  _uint    ref      37      37   >>  16
  _double  ref      42      41   >>  18
  _fixnum  ref     509     510   >>  88
  _racket  ref     373     373   >>  96
 from/to bytes
  _ulong   ref      29      29   >>  11
  _ulong   set!    629  >>  62   >>  11
struct ref         171     170    > 164
struct set!        660  >> 180    > 172
math               105   >  84    >  64
plus                29      28   >>  13
strlen              19      19    >  14
draw               228     227      213

There's still room for improvement in foreign calls. A Chez Scheme variant of plus runs in 3ms instead of 13ms, which reflects overhead still added by Racket's more dynamic FFI. The round of improvements here seems on the path to better improvement, though.

5 Likes