From 48c4717f30cc1f83d02f045c3b47a2885863bff2 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Mon, 27 Apr 2015 09:45:12 +0200 Subject: [PATCH] x86/fpu: Optimize fpu__save() So fpu__save() does this currently: copy_fpregs_to_fpstate(fpu); if (!use_eager_fpu()) fpregs_deactivate(fpu); ... which deactivates the FPU on lazy switching systems unconditionally. Both usecases of fpu__save() use this function to save the FPU state into a fpstate: fork()/clone() and math error signal handling. The unconditional disabling of FPU registers in the lazy switching case is probably a mistaken conversion of old FNSAVE code (that had to disable FPU registers). So speed up this code by only disabling FPU registers when absolutely necessary: when indicated by the copy_fpregs_to_fpstate() return code: if (!copy_fpregs_to_fpstate(fpu)) fpregs_deactivate(fpu); Reviewed-by: Borislav Petkov Cc: Andy Lutomirski Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar --- arch/x86/kernel/fpu/core.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index a0b2221b686d..b1fbbb8eb934 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -170,7 +170,7 @@ void irq_ts_restore(int TS_state) EXPORT_SYMBOL_GPL(irq_ts_restore); /* - * Save the FPU state (initialize it if necessary): + * Save the FPU state (mark it for reload if necessary): * * This only ever gets called for the current task. */ @@ -180,8 +180,7 @@ void fpu__save(struct fpu *fpu) preempt_disable(); if (fpu->fpregs_active) { - copy_fpregs_to_fpstate(fpu); - if (!use_eager_fpu()) + if (!copy_fpregs_to_fpstate(fpu)) fpregs_deactivate(fpu); } preempt_enable(); -- 2.34.1