Messages in this thread Patch in this message | | | From | "Fenghua Yu" <> | Subject | [PATCH v3 Bugfix 5/6] x86/xsaves: Keep xstate_bv in init_xstate_buf header as zero for init optimimization | Date | Fri, 8 May 2015 14:31:04 -0700 |
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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
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