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Date: Mon, 4 Oct 2021 23:04:11 +0800
From: Greentime Hu <greentime.hu@...ive.com>
To: Jisheng Zhang <jszhang3@...l.ustc.edu.cn>
Cc: linux-riscv <linux-riscv@...ts.infradead.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Albert Ou <aou@...s.berkeley.edu>,
Palmer Dabbelt <palmer@...belt.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Vincent Chen <vincent.chen@...ive.com>
Subject: Re: [RFC PATCH v8 21/21] riscv: Turn has_vector into a static key if VECTOR=y
Jisheng Zhang <jszhang3@...l.ustc.edu.cn> 於 2021年9月15日 週三 下午10:31寫道：
>
> On Thu, 9 Sep 2021 01:45:33 +0800
> Greentime Hu <greentime.hu@...ive.com> wrote:
>
> > Just like fpu, we can use static key for has_vector.
> > The has_vector check sits at hot code path: switch_to(). Currently,
> > has_vector is a bool variable if VECTOR=y, switch_to() checks it each time,
> > we can optimize out this check by turning the has_vector into a static key.
> >
>
> has_vector is newly introduced in this patch set so I believe this patch can
> be folded into has_vector introducing patch, I.E patch 6
>
ok, I'll split this patch and merge these codes into its related patches.
>
> > Signed-off-by: Greentime Hu <greentime.hu@...ive.com>
> > ---
> > arch/riscv/include/asm/switch_to.h | 10 +++++++---
> > arch/riscv/kernel/cpufeature.c | 4 ++--
> > arch/riscv/kernel/kernel_mode_vector.c | 4 ++--
> > arch/riscv/kernel/process.c | 8 ++++----
> > arch/riscv/kernel/signal.c | 6 +++---
> > 5 files changed, 18 insertions(+), 14 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
> > index b48c9c974564..576204217e0f 100644
> > --- a/arch/riscv/include/asm/switch_to.h
> > +++ b/arch/riscv/include/asm/switch_to.h
> > @@ -71,7 +71,11 @@ static __always_inline bool has_fpu(void) { return false; }
> > #endif
> >
> > #ifdef CONFIG_VECTOR
> > -extern bool has_vector;
> > +extern struct static_key_false cpu_hwcap_vector;
> > +static __always_inline bool has_vector(void)
> > +{
> > + return static_branch_likely(&cpu_hwcap_vector);
> > +}
> > extern unsigned long riscv_vsize;
> > extern void __vstate_save(struct __riscv_v_state *save_to, void *datap);
> > extern void __vstate_restore(struct __riscv_v_state *restore_from, void *datap);
> > @@ -120,7 +124,7 @@ static inline void __switch_to_vector(struct task_struct *prev,
> > }
> >
> > #else
> > -#define has_vector false
> > +static __always_inline bool has_vector(void) { return false; }
> > #define riscv_vsize (0)
> > #define vstate_save(task, regs) do { } while (0)
> > #define vstate_restore(task, regs) do { } while (0)
> > @@ -136,7 +140,7 @@ do { \
> > struct task_struct *__next = (next); \
> > if (has_fpu()) \
> > __switch_to_fpu(__prev, __next); \
> > - if (has_vector) \
> > + if (has_vector()) \
> > __switch_to_vector(__prev, __next); \
> > ((last) = __switch_to(__prev, __next)); \
> > } while (0)
> > diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> > index af984f875f60..0139ec20adce 100644
> > --- a/arch/riscv/kernel/cpufeature.c
> > +++ b/arch/riscv/kernel/cpufeature.c
> > @@ -23,7 +23,7 @@ __ro_after_init DEFINE_STATIC_KEY_FALSE(cpu_hwcap_fpu);
> > #endif
> > #ifdef CONFIG_VECTOR
> > #include <asm/vector.h>
> > -bool has_vector __read_mostly;
> > +__ro_after_init DEFINE_STATIC_KEY_FALSE(cpu_hwcap_vector);
> > unsigned long riscv_vsize __read_mostly;
> > #endif
> >
> > @@ -157,7 +157,7 @@ void __init riscv_fill_hwcap(void)
> >
> > #ifdef CONFIG_VECTOR
> > if (elf_hwcap & COMPAT_HWCAP_ISA_V) {
> > - has_vector = true;
> > + static_branch_enable(&cpu_hwcap_vector);
> > /* There are 32 vector registers with vlenb length. */
> > rvv_enable();
> > riscv_vsize = csr_read(CSR_VLENB) * 32;
> > diff --git a/arch/riscv/kernel/kernel_mode_vector.c b/arch/riscv/kernel/kernel_mode_vector.c
> > index 0d990bd8b8dd..0d08954c30af 100644
> > --- a/arch/riscv/kernel/kernel_mode_vector.c
> > +++ b/arch/riscv/kernel/kernel_mode_vector.c
> > @@ -110,7 +110,7 @@ static void vector_flush_cpu_state(void)
> > */
> > void kernel_rvv_begin(void)
> > {
> > - if (WARN_ON(!has_vector))
> > + if (WARN_ON(!has_vector()))
> > return;
> >
> > WARN_ON(!may_use_vector());
> > @@ -140,7 +140,7 @@ EXPORT_SYMBOL(kernel_rvv_begin);
> > */
> > void kernel_rvv_end(void)
> > {
> > - if (WARN_ON(!has_vector))
> > + if (WARN_ON(!has_vector()))
> > return;
> >
> > /* Invalidate vector regs */
> > diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> > index 05ff5f934e7e..62540815ba1c 100644
> > --- a/arch/riscv/kernel/process.c
> > +++ b/arch/riscv/kernel/process.c
> > @@ -96,7 +96,7 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
> > fstate_restore(current, regs);
> > }
> >
> > - if (has_vector) {
> > + if (has_vector()) {
> > struct __riscv_v_state *vstate = &(current->thread.vstate);
> >
> > /* Enable vector and allocate memory for vector registers. */
> > @@ -141,11 +141,11 @@ void flush_thread(void)
> > int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
> > {
> > fstate_save(src, task_pt_regs(src));
> > - if (has_vector)
> > + if (has_vector())
> > /* To make sure every dirty vector context is saved. */
> > vstate_save(src, task_pt_regs(src));
> > *dst = *src;
> > - if (has_vector) {
> > + if (has_vector()) {
> > /* Copy vector context to the forked task from parent. */
> > if ((task_pt_regs(src)->status & SR_VS) != SR_VS_OFF) {
> > dst->thread.vstate.datap = kzalloc(riscv_vsize, GFP_KERNEL);
> > @@ -164,7 +164,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
> > void arch_release_task_struct(struct task_struct *tsk)
> > {
> > /* Free the vector context of datap. */
> > - if (has_vector)
> > + if (has_vector())
> > kfree(tsk->thread.vstate.datap);
> > }
> >
> > diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
> > index d30a3b588156..6a19b4b7b206 100644
> > --- a/arch/riscv/kernel/signal.c
> > +++ b/arch/riscv/kernel/signal.c
> > @@ -192,7 +192,7 @@ static long restore_sigcontext(struct pt_regs *regs,
> > goto invalid;
> > goto done;
> > case RVV_MAGIC:
> > - if (!has_vector)
> > + if (!has_vector())
> > goto invalid;
> > if (size != rvv_sc_size)
> > goto invalid;
> > @@ -221,7 +221,7 @@ static size_t cal_rt_frame_size(void)
> >
> > frame_size = sizeof(*frame);
> >
> > - if (has_vector)
> > + if (has_vector())
> > total_context_size += rvv_sc_size;
> > /* Preserved a __riscv_ctx_hdr for END signal context header. */
> > total_context_size += sizeof(struct __riscv_ctx_hdr);
> > @@ -288,7 +288,7 @@ static long setup_sigcontext(struct rt_sigframe __user *frame,
> > if (has_fpu())
> > err |= save_fp_state(regs, &sc->sc_fpregs);
> > /* Save the vector state. */
> > - if (has_vector)
> > + if (has_vector())
> > err |= save_v_state(regs, &sc_reserved_free_ptr);
> >
> > /* Put END __riscv_ctx_hdr at the end. */
>
>
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