Unverified Commit 37a7a2a1 authored by Jisheng Zhang's avatar Jisheng Zhang Committed by Palmer Dabbelt
Browse files

riscv: Turn has_fpu into a static key if FPU=y 



The has_fpu check sits at hot code path: switch_to(). Currently, has_fpu
is a bool variable if FPU=y, switch_to() checks it each time, we can
optimize out this check by turning the has_fpu into a static key.

Signed-off-by: default avatarJisheng Zhang <jszhang@kernel.org>
Signed-off-by: default avatarPalmer Dabbelt <palmerdabbelt@google.com>
parent 8237c524

arch/riscv/include/asm/switch_to.h

+8 −3
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ 
#ifndef _ASM_RISCV_SWITCH_TO_H

#define _ASM_RISCV_SWITCH_TO_H



#include <linux/jump_label.h>

#include <linux/sched/task_stack.h>

#include <asm/processor.h>

#include <asm/ptrace.h>
@@ -55,9 +56,13 @@ static inline void __switch_to_aux(struct task_struct *prev, 
	fstate_restore(next, task_pt_regs(next));

}



extern bool has_fpu;

extern struct static_key_false cpu_hwcap_fpu;

static __always_inline bool has_fpu(void)

{

	return static_branch_likely(&cpu_hwcap_fpu);

}

#else

#define has_fpu false

static __always_inline bool has_fpu(void) { return false; }

#define fstate_save(task, regs) do { } while (0)

#define fstate_restore(task, regs) do { } while (0)

#define __switch_to_aux(__prev, __next) do { } while (0)
@@ -70,7 +75,7 @@ extern struct task_struct *__switch_to(struct task_struct *, 
do {							\

	struct task_struct *__prev = (prev);		\

	struct task_struct *__next = (next);		\

	if (has_fpu)					\

	if (has_fpu())					\

		__switch_to_aux(__prev, __next);	\

	((last) = __switch_to(__prev, __next));		\

} while (0)

arch/riscv/kernel/cpufeature.c

+2 −2
Original line number Diff line number Diff line
@@ -19,7 +19,7 @@ unsigned long elf_hwcap __read_mostly; 
static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;



#ifdef CONFIG_FPU

bool has_fpu __read_mostly;

__ro_after_init DEFINE_STATIC_KEY_FALSE(cpu_hwcap_fpu);

#endif



/**
@@ -146,6 +146,6 @@ void riscv_fill_hwcap(void) 


#ifdef CONFIG_FPU

	if (elf_hwcap & (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D))

		has_fpu = true;

		static_branch_enable(&cpu_hwcap_fpu);

#endif

}

arch/riscv/kernel/process.c

+1 −1
Original line number Diff line number Diff line
@@ -87,7 +87,7 @@ void start_thread(struct pt_regs *regs, unsigned long pc, 
	unsigned long sp)

{

	regs->status = SR_PIE;

	if (has_fpu) {

	if (has_fpu()) {

		regs->status |= SR_FS_INITIAL;

		/*

		 * Restore the initial value to the FP register

arch/riscv/kernel/signal.c

+2 −2
Original line number Diff line number Diff line
@@ -90,7 +90,7 @@ static long restore_sigcontext(struct pt_regs *regs, 
	/* sc_regs is structured the same as the start of pt_regs */

	err = __copy_from_user(regs, &sc->sc_regs, sizeof(sc->sc_regs));

	/* Restore the floating-point state. */

	if (has_fpu)

	if (has_fpu())

		err |= restore_fp_state(regs, &sc->sc_fpregs);

	return err;

}
@@ -143,7 +143,7 @@ static long setup_sigcontext(struct rt_sigframe __user *frame, 
	/* sc_regs is structured the same as the start of pt_regs */

	err = __copy_to_user(&sc->sc_regs, regs, sizeof(sc->sc_regs));

	/* Save the floating-point state. */

	if (has_fpu)

	if (has_fpu())

		err |= save_fp_state(regs, &sc->sc_fpregs);

	return err;

}