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, 4 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index 96950f189b5a..7b291707eb31 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -814,7 +814,9 @@ int handle_rt_signal32(struct ksignal *ksig, sigset_t *oldset,
 	}
 	regs->link = tramp;
 
+#ifdef CONFIG_PPC_FPU_REGS
 	tsk->thread.fp_state.fpscr = 0;	/* turn off all fp exceptions */
+#endif
 
 	/* create a stack frame for the caller of the handler */
 	newsp = ((unsigned long)rt_sf) - (__SIGNAL_FRAMESIZE + 16);
@@ -1271,7 +1273,9 @@ int handle_signal32(struct ksignal *ksig, sigset_t *oldset,
 
 	regs->link = tramp;
 
+#ifdef CONFIG_PPC_FPU_REGS
 	tsk->thread.fp_state.fpscr = 0;	/* turn off all fp exceptions */
+#endif
 
 	/* create a stack frame for the caller of the handler */
 	newsp = ((unsigned long)frame) - __SIGNAL_FRAMESIZE;