1. 24 11月, 2009 1 次提交
    • G
      sh: add sleazy FPU optimization · a0458b07
      Giuseppe CAVALLARO 提交于
      sh port of the sLeAZY-fpu feature currently implemented for some architectures
      such us i386.
      
      Right now the SH kernel has a 100% lazy fpu behaviour.
      This is of course great for applications that have very sporadic or no FPU use.
      However for very frequent FPU users...  you take an extra trap every context
      switch.
      The patch below adds a simple heuristic to this code: after 5 consecutive
      context switches of FPU use, the lazy behavior is disabled and the context
      gets restored every context switch.
      After 256 switches, this is reset and the 100% lazy behavior is returned.
      
      Tests with LMbench showed no regression.
      I saw a little improvement due to the prefetching (~2%).
      
      The tests below also show that, with this sLeazy patch, indeed,
      the number of FPU exceptions is reduced.
      To test this. I hacked the lat_ctx LMBench to use the FPU a little more.
      
         sLeasy implementation
         ===========================================
         switch_to calls            |  79326
         sleasy   calls             |  42577
         do_fpu_state_restore  calls|  59232
         restore_fpu   calls        |  59032
      
         Exceptions:  0x800 (FPU disabled  ): 16604
      
         100% Leazy (default implementation)
         ===========================================
         switch_to  calls            |  79690
         do_fpu_state_restore calls  |  53299
         restore_fpu  calls          |   53101
      
         Exceptions: 0x800 (FPU disabled  ):  53273
      Signed-off-by: NGiuseppe Cavallaro <peppe.cavallaro@st.com>
      Signed-off-by: NStuart Menefy <stuart.menefy@st.com>
      Signed-off-by: NPaul Mundt <lethal@linux-sh.org>
      a0458b07
  2. 20 11月, 2009 9 次提交
  3. 19 11月, 2009 11 次提交
  4. 18 11月, 2009 19 次提交