1. 06 Feb, 2007 1 commit
    • Chen, Kenneth W's avatar
      [IA64] remove per-cpu ia64_phys_stacked_size_p8 · a0776ec8
      Chen, Kenneth W authored
      It's not efficient to use a per-cpu variable just to store
      how many physical stack register a cpu has.  Ever since the
      incarnation of ia64 up till upcoming Montecito processor, that
      variable has "glued" to 96. Having a variable in memory means
      that the kernel is burning an extra cacheline access on every
      syscall and kernel exit path.  Such "static" value is better
      served with the instruction patching utility exists today.
      Convert ia64_phys_stacked_size_p8 into dynamic insn patching.
      
      This also has a pleasant side effect of eliminating access to
      per-cpu area while psr.ic=0 in the kernel exit path. (fixable
      for per-cpu DTC work, but why bother?)
      
      There are some concerns with the default value that the instruc-
      tion encoded in the kernel image.  It shouldn't be concerned.
      The reasons are:
      
      (1) cpu_init() is called at CPU initialization.  In there, we
          find out physical stack register size from PAL and patch
          two instructions in kernel exit code.  The code in question
          can not be executed before the patching is done.
      
      (2) current implementation stores zero in ia64_phys_stacked_size_p8,
          and that's what the current kernel exit path loads the value with.
          With the new code, it is equivalent that we store reg size 96
          in ia64_phys_stacked_size_p8, thus creating a better safety net.
          Given (1) above can never fail, having (2) is just a bonus.
      
      All in all, this patch allow one less memory reference in the kernel
      exit path, thus reducing syscall and interrupt return latency; and
      avoid polluting potential useful data in the CPU cache.
      Signed-off-by: default avatarKen Chen <kenneth.w.chen@intel.com>
      Signed-off-by: default avatarTony Luck <tony.luck@intel.com>
      a0776ec8
  2. 04 Feb, 2007 3 commits
  3. 03 Feb, 2007 11 commits
  4. 02 Feb, 2007 25 commits