Commit-ID: 2729818f35c9b1a1614624e2edcd3e80c59c8689 Gitweb: http://git.kernel.org/tip/2729818f35c9b1a1614624e2edcd3e80c59c8689 Author: Fenghua Yu <[email protected]> AuthorDate: Fri, 20 May 2016 10:47:07 -0700 Committer: Ingo Molnar <[email protected]> CommitDate: Fri, 17 Jun 2016 10:10:23 +0200
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 <[email protected]> Signed-off-by: Yu-cheng Yu <[email protected]> Reviewed-by: Dave Hansen <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Brian Gerst <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Denys Vlasenko <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Quentin Casasnovas <[email protected]> Cc: Ravi V. Shankar <[email protected]> Cc: Sai Praneeth Prakhya <[email protected]> Cc: Thomas Gleixner <[email protected]> Link: http://lkml.kernel.org/r/2fb4ec7f18b76e8cda057a8c0038def74a9b8044.1463760376.git.yu-cheng...@intel.com Signed-off-by: Ingo Molnar <[email protected]> --- 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);
