From: Fenghua Yu <fenghua...@intel.com>
Keep init_fpstate.xsave.header.xfeatures 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 XRSTOR/XRSTORS instruction. This largely impacts context switch
performance.
Signed-off-by: Fenghua Yu <fenghua...@intel.com>
Signed-off-by: Yu-cheng Yu <yu-cheng...@intel.com>
Reviewed-by: Dave Hansen <dave.han...@intel.com>
---
arch/x86/kernel/fpu/xstate.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 875afe9..5239d4d 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -329,13 +329,11 @@ static void __init setup_init_fpu_buf(void)
setup_xstate_features();
print_xstate_features();
- if (cpu_has_xsaves) {
+ if (cpu_has_xsaves)
init_fpstate.xsave.header.xcomp_bv = (u64)1 << 63 |
xfeatures_mask;
- init_fpstate.xsave.header.xfeatures = xfeatures_mask;
- }
/*
- * Init all the features state with header_bv being 0x0
+ * Init all the features state with header.xfeatures being 0x0
*/
copy_kernel_to_xregs_booting(&init_fpstate.xsave);
--
1.9.1
