lkml.org 
[lkml]   [2011]   [Oct]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH RFC V2 3/5] jump_label: if a key has already been initialized, don't nop it out
    On 10/06/2011 11:13 AM, H. Peter Anvin wrote:
    > On 10/06/2011 11:10 AM, Jason Baron wrote:
    >> It would be cool if we could make the total width 2-bytes, when
    >> possible. It might be possible by making the initial 'JUMP_LABEL_INITIAL_NOP'
    >> as a 'jmp' to the 'l_yes' label. And then patching that with a no-op at boot
    >> time or link time - letting the compiler pick the width. In that way we could
    >> get the optimal width...
    >>
    > Yes, that would be a win just based on icache footprint alone.

    I'm not sure it would be a win, necessarily. My test with back-to-back
    jmp2 was definitely slower than with the nop padding it out to 5 bytes;
    I suspect that's a result of having too many jmps within one cacheline.
    Of course, there's no reason why the CPU would optimise for jumps to
    jumps, so perhaps its just hitting a "stupid programmer" path.

    J


    \
     
     \ /
      Last update: 2011-10-06 23:43    [W:4.054 / U:0.312 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site