powerpc/signal: Don't manage floating point regs when no FPU

There is no point in copying floating point regs when there
is no FPU and MATH_EMULATION is not selected.

Create a new CONFIG_PPC_FPU_REGS bool that is selected by
CONFIG_MATH_EMULATION and CONFIG_PPC_FPU, and use it to
opt out everything related to fp_state in thread_struct.

The asm const used only by fpu.S are opted out with CONFIG_PPC_FPU
as fpu.S build is conditionnal to CONFIG_PPC_FPU.

The following app spends approx 8.1 seconds system time on an 8xx
without the patch, and 7.0 seconds with the patch (13.5% reduction).

On an 832x, it spends approx 2.6 seconds system time without
the patch and 2.1 seconds with the patch (19% reduction).

	void sigusr1(int sig) { }

	int main(int argc, char **argv)
	{
		int i = 100000;

		signal(SIGUSR1, sigusr1);
		for (;i--;)
			raise(SIGUSR1);
		exit(0);
	}

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/7569070083e6cd5b279bb5023da601aba3c06f3c.1597770847.git.christophe.leroy@csgroup.eu

1 files changed, 13 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/signal.h b/arch/powerpc/kernel/signal.h
index 4626d39cc0f0..6c2a33ab042c 100644
--- a/arch/powerpc/kernel/signal.h
+++ b/arch/powerpc/kernel/signal.h
@@ -34,7 +34,7 @@ unsigned long copy_fpr_to_user(void __user *to, struct task_struct *task);
 unsigned long copy_ckfpr_to_user(void __user *to, struct task_struct *task);
 unsigned long copy_fpr_from_user(struct task_struct *task, void __user *from);
 unsigned long copy_ckfpr_from_user(struct task_struct *task, void __user *from);
-#else
+#elif defined(CONFIG_PPC_FPU_REGS)
 static inline unsigned long
 copy_fpr_to_user(void __user *to, struct task_struct *task)
 {
@@ -63,6 +63,18 @@ copy_ckfpr_from_user(struct task_struct *task, void __user *from)
 				ELF_NFPREG * sizeof(double));
 }
 #endif /* CONFIG_PPC_TRANSACTIONAL_MEM */
+#else
+static inline unsigned long
+copy_fpr_to_user(void __user *to, struct task_struct *task)
+{
+	return 0;
+}
+
+static inline unsigned long
+copy_fpr_from_user(struct task_struct *task, void __user *from)
+{
+	return 0;
+}
 #endif
 
 #ifdef CONFIG_PPC64