% perl tailbm -30 100 721994.lines 
Benchmark: running f_rb_obj, f_rb_obj_u, f_rb_tie, f_rb_tie_u, file_tail, grinder, each for at least 30 CPU seconds...
  f_rb_obj:  54 wallclock secs (30.52 usr +  0.93 sys = 31.45 CPU) @ 147.31/s (n=4633)
f_rb_obj_u:  70 wallclock secs (30.24 usr +  0.83 sys = 31.07 CPU) @ 144.19/s (n=4480)
  f_rb_tie:  69 wallclock secs (30.70 usr +  0.60 sys = 31.30 CPU) @ 121.31/s (n=3797)
f_rb_tie_u:  68 wallclock secs (29.96 usr +  0.53 sys = 30.49 CPU) @ 118.99/s (n=3628)
 file_tail:  76 wallclock secs (31.02 usr +  0.83 sys = 31.85 CPU) @ 60.60/s (n=1930)
   grinder: 121 wallclock secs (33.17 usr +  2.10 sys = 35.27 CPU) @  0.09/s (n=3)
            (warning: too few iterations for a reliable count)
     lastn:  40 wallclock secs (20.15 usr + 10.80 sys = 30.95 CPU) @ 19.48/s (n=603)
lastn_getc:  42 wallclock secs (18.05 usr + 13.81 sys = 31.86 CPU) @ 17.70/s (n=564)