% perl tailbm -30 10 100.lines 

Benchmark: running f_rb_obj, f_rb_obj_u, f_rb_tie, f_rb_tie_u, file_tail, grinder, lastn, lastn_getc, each for at least 30 CPU seconds...
  f_rb_obj:  75 wallclock secs (28.61 usr +  2.71 sys = 31.32 CPU) @ 807.15/s (n=25280)
f_rb_obj_u:  70 wallclock secs (28.59 usr +  2.75 sys = 31.34 CPU) @ 806.32/s (n=25270)
  f_rb_tie:  70 wallclock secs (29.45 usr +  2.37 sys = 31.82 CPU) @ 719.96/s (n=22909)
f_rb_tie_u:  74 wallclock secs (29.05 usr +  2.44 sys = 31.49 CPU) @ 729.76/s (n=22980)
 file_tail: 112 wallclock secs (29.71 usr +  2.34 sys = 32.05 CPU) @ 274.26/s (n=8790)
   grinder:  74 wallclock secs (28.38 usr +  2.77 sys = 31.15 CPU) @ 566.52/s (n=17647)
     lastn:  69 wallclock secs (19.78 usr + 11.34 sys = 31.12 CPU) @ 22.88/s (n=712)
lastn_getc:  77 wallclock secs (18.88 usr + 13.17 sys = 32.05 CPU) @ 19.78/s (n=634)