Commits on May 3, 2019

1. Check the pattern before anything else, since it doesn't require meta… …

   …data
   
   This should partially address sharkdp#432 by decreasing the number of stat() calls:
   
       $ strace -c -f ./fd-before '\.h$' /usr -j1 -S +1k >/dev/null
       % time     seconds  usecs/call     calls    errors syscall
       ------ ----------- ----------- --------- --------- ----------------
        15.71    8.831948           7   1192279     46059 stat
       $ strace -c -f ./fd-after '\.h$' /usr -j1 -S +1k >/dev/null
       % time     seconds  usecs/call     calls    errors syscall
       ------ ----------- ----------- --------- --------- ----------------
         7.92    1.972474          10    183907     46046 stat
   
   Though it's not as few as possible:
   
       $ strace -c -f find /usr -iname '*.h' -size +1k >/dev/null
       % time     seconds  usecs/call     calls    errors syscall
       ------ ----------- ----------- --------- --------- ----------------
        19.01    0.946500           5    161649           newfstatat
       $ strace -c -f bfs /usr -iname '*.h' -size +1k >/dev/null
       % time     seconds  usecs/call     calls    errors syscall
       ------ ----------- ----------- --------- --------- ----------------
        13.73    0.406565           5     69005           statx
   
   Performance is much better when metadata is required:
   
       $ hyperfine ./fd-{before,after}" '\.h$' /usr -j1 -S +1k"
       Benchmark sharkdp#1: ./fd-before '\.h$' /usr -j1 -S +1k
         Time (mean ± σ):      4.623 s ±  0.154 s    [User: 1.465 s, System: 3.354 s]
         Range (min … max):    4.327 s …  4.815 s    10 runs
   
       Benchmark sharkdp#2: ./fd-after '\.h$' /usr -j1 -S +1k
         Time (mean ± σ):      2.650 s ±  0.058 s    [User: 1.258 s, System: 1.592 s]
         Range (min … max):    2.568 s …  2.723 s    10 runs
   
       Summary
         './fd-after '\.h$' /usr -j1 -S +1k' ran
           1.74 ± 0.07 times faster than './fd-before '\.h$' /usr -j1 -S +1k'
   
   While remaining the same when it's not:
   
       $ hyperfine ./fd-{before,after}" '\.h$' /usr -j1"
       Benchmark sharkdp#1: ./fd-before '\.h$' /usr -j1
         Time (mean ± σ):      2.382 s ±  0.038 s    [User: 1.221 s, System: 1.286 s]
         Range (min … max):    2.325 s …  2.433 s    10 runs
   
       Benchmark sharkdp#2: ./fd-after '\.h$' /usr -j1
         Time (mean ± σ):      2.362 s ±  0.034 s    [User: 1.193 s, System: 1.294 s]
         Range (min … max):    2.307 s …  2.422 s    10 runs
   
       Summary
         './fd-after '\.h$' /usr -j1' ran
           1.01 ± 0.02 times faster than './fd-before '\.h$' /usr -j1'

   

   tavianator committed May 3, 2019
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