From 7d9370607d28afd454775c623d5447603473a3c3 Mon Sep 17 00:00:00 2001 From: Fenghua Yu Date: Fri, 20 May 2016 10:47:07 -0700 Subject: [PATCH] x86/fpu/xstate: Keep init_fpstate.xsave.header.xfeatures as zero for init optimization 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 Signed-off-by: Yu-cheng Yu Reviewed-by: Dave Hansen Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Dave Hansen Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Quentin Casasnovas Cc: Ravi V. Shankar Cc: Sai Praneeth Prakhya Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/2fb4ec7f18b76e8cda057a8c0038def74a9b8044.1463760376.git.yu-cheng.yu@intel.com Signed-off-by: Ingo Molnar --- 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 46abfaf..dbfef1b 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 (boot_cpu_has(X86_FEATURE_XSAVES)) { + if (boot_cpu_has(X86_FEATURE_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); -- 2.7.4