lkml.org 
[lkml]   [2015]   [May]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[PATCH v3 Bugfix 5/6] x86/xsaves: Keep xstate_bv in init_xstate_buf header as zero for init optimimization
    Date
    From: Fenghua Yu <fenghua.yu@intel.com>

    Keep xstate_bv in init_xstate_buf header as zero for init optimization.
    This is important for init optimization that is implemented in processor.
    If a bit corresponding to an xstate in xstate_bv is 0, it means the
    xstate is in init status and will not be read from memory to the processor
    during xrestor* instruction. This largely impacts context switch
    performance.

    Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
    Reviewed-by: Dave Hansen <dave.hansen@intel.com>
    ---
    arch/x86/kernel/xsave.c | 10 +++++++---
    1 file changed, 7 insertions(+), 3 deletions(-)

    diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
    index 4217bec..547f293 100644
    --- a/arch/x86/kernel/xsave.c
    +++ b/arch/x86/kernel/xsave.c
    @@ -545,6 +545,12 @@ static void __init setup_init_fpu_buf(void)
    */
    init_xstate_buf = alloc_bootmem_align(kernel_xstate_size,
    __alignof__(struct xsave_struct));
    +
    + /*
    + * Make sure xstate_bv is zero to allow init optimization work.
    + */
    + init_xstate_buf->xsave_hdr.xstate_bv = 0;
    +
    fx_finit(&init_xstate_buf->i387);

    if (!cpu_has_xsave)
    @@ -552,11 +558,9 @@ static void __init setup_init_fpu_buf(void)

    setup_xstate_features();

    - if (cpu_has_xsaves) {
    + if (cpu_has_xsaves)
    init_xstate_buf->xsave_hdr.xcomp_bv =
    (u64)1 << 63 | pcntxt_mask;
    - init_xstate_buf->xsave_hdr.xstate_bv = pcntxt_mask;
    - }

    /*
    * Init all the features state with header_bv being 0x0
    --
    1.8.1.2


    \
     
     \ /
      Last update: 2015-05-09 00:01    [W:3.647 / U:0.764 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site