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 <b...@alien8.de> Cc: Andy Lutomirski <l...@amacapital.net> Cc: Dave Hansen <dave.han...@linux.intel.com> Cc: Fenghua Yu <fenghua...@intel.com> Cc: H. Peter Anvin <h...@zytor.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Oleg Nesterov <o...@redhat.com> Cc: Thomas Gleixner <t...@linutronix.de> Signed-off-by: Ingo Molnar <mi...@kernel.org> --- 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 1e79a6b3fc27..8835b802aa16 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(); -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/