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

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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: Jisheng Zhang <jszhang@kernel.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
This commit is contained in:
Jisheng Zhang 2021-05-12 22:55:45 +08:00 committed by Palmer Dabbelt
parent 8237c5243a
commit 37a7a2a10e
No known key found for this signature in database
GPG Key ID: 2E1319F35FBB1889
4 changed files with 13 additions and 8 deletions
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11
arch/riscv/include/asm/switch_to.h
View File

@ -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)

4
arch/riscv/kernel/cpufeature.c
View File

@ -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
}

2
arch/riscv/kernel/process.c
View File

@ -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

4
arch/riscv/kernel/signal.c
View File

@ -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;
}