x86/fpu: Print out whether we are doing lazy/eager FPU context switches

Ever since the kernel started defaulting to eager FPU switches on modern Intel
CPUs it's not been obvious whether a given system is using the lazy or the eager
FPU context switching logic.

So generate a boot message about which mode the FPU code is in:

  x86/fpu: Using 'lazy' FPU context switches.

or:

  x86/fpu: Using 'eager' FPU context switches.

Reviewed-by: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/fpu/xsave.c b/arch/x86/kernel/fpu/xsave.c
index a52205b87acb1861a966dc8d2fbc03327ee837c6..61696c5005eb98696471a6d4010315686e36394e 100644 (file)
--- a/arch/x86/kernel/fpu/xsave.c
+++ b/arch/x86/kernel/fpu/xsave.c
@@ -691,6 +691,8 @@ void __init_refok eager_fpu_init(void)
        if (eagerfpu == ENABLE)
                setup_force_cpu_cap(X86_FEATURE_EAGER_FPU);
 
+       printk_once(KERN_INFO "x86/fpu: Using '%s' FPU context switches.\n", eagerfpu == ENABLE ? "eager" : "lazy");
+
        if (!cpu_has_eager_fpu) {
                stts();
                return;