O_DIRECT Numbers

I benchmarked the advantage of bypassing the cache on a x86 low end 2-way SMP box, with 128Mbytes of RAM and one IDE disk with a bandwidth of around 15Mbytes/sec, using bonnie on a 400Mbytes file.
buffered IO

              -------Sequential Output-------- ---Sequential Input-- --Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
           MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU  /sec %CPU
          400  xxxx xxxx 12999 12.1  5918 10.8  xxxx xxxx 13412 12.1   xxx  xxx
          400  xxxx xxxx 12960 12.3  5896 11.1  xxxx xxxx 13520 13.3   xxx  xxx

direct IO
              -------Sequential Output-------- ---Sequential Input-- --Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
           MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU  /sec %CPU
          400  xxxx xxxx 12810  1.8  5855  1.6  xxxx xxxx 13529  1.2   xxx  xxx
          400  xxxx xxxx 12814  1.8  5866  1.7  xxxx xxxx 13519  1.3   xxx  xxx