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

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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
This commit is contained in:
Christophe Leroy
2020-08-18 17:19:17 +00:00
committed by Michael Ellerman
parent 4d90eb97e2
commit b6254ced4d
11 changed files with 50 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
arch/powerpc/kernel/traps.c
View File

@@ -1190,7 +1190,9 @@ static void parse_fpe(struct pt_regs *regs)
flush_fp_to_thread(current);
#ifdef CONFIG_PPC_FPU_REGS
code = __parse_fpscr(current->thread.fp_state.fpscr);
#endif
_exception(SIGFPE, regs, code, regs->nip);
}