[PATCH 0/2] introduce unified static key mechanism for ISA ext

[PATCH 0/2] introduce unified static key mechanism for ISA ext

[Jisheng Zhang]

Currently, riscv has several extensions which may not be supported on all
riscv platforms, for example, FPU and so on. To support unified kernel
Image style, we need to check whether the feature is suportted or not.
If the check sits at hot code path, the performance will be impacted a
lot. static key can be used to solve the issue. In the past, FPU
support has been converted to use static key mechanism. I believe we
will have similar cases in the future.

Jisheng Zhang (2):
  riscv: introduce unified static key mechanism for ISA extensions
  riscv: switch has_fpu() to the unified static key mechanism

 arch/riscv/include/asm/hwcap.h     | 40 ++++++++++++++++++++++++++++++
 arch/riscv/include/asm/switch_to.h |  5 ++--
 arch/riscv/kernel/cpufeature.c     | 14 +++++------
 3 files changed, 50 insertions(+), 9 deletions(-)

-- 
2.34.1


_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

[PATCH 1/2] riscv: introduce unified static key mechanism for ISA extensions

[Jisheng Zhang]

Currently, riscv has several extensions which may not be supported on
all riscv platforms, for example, FPU and so on. To support unified
kernel Image style, we need to check whether the feature is suportted
or not. If the check sits at hot code path, then performance will be
impacted a lot. static key can be used to solve the issue. In the past
FPU support has been converted to use static key mechanism. I believe
we will have similar cases in the future.

this patch tries to add an unified mechanism to use static keys for
some ISA extensions by implementing an array of default-false static keys
and enabling them when detected.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 arch/riscv/include/asm/hwcap.h | 40 ++++++++++++++++++++++++++++++++++
 arch/riscv/kernel/cpufeature.c |  7 ++++++
 2 files changed, 47 insertions(+)

diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index 0734e42f74f2..b0433d2b880d 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -12,6 +12,7 @@
 #include <uapi/asm/hwcap.h>
 
 #ifndef __ASSEMBLY__
+#include <linux/jump_label.h>
 /*
  * This yields a mask that user programs can use to figure out what
  * instruction set this cpu supports.
@@ -55,6 +56,16 @@ enum riscv_isa_ext_id {
 	RISCV_ISA_EXT_ID_MAX = RISCV_ISA_EXT_MAX,
 };
 
+/*
+ * This enum represents the logical ID for each RISC-V ISA extension static
+ * keys. We can use static key to optimize code path if some ISA extensions
+ * are available.
+ */
+enum riscv_isa_ext_key {
+	RISCV_ISA_EXT_KEY_FPU,		/* For 'F' and 'D' */
+	RISCV_ISA_EXT_KEY_MAX,
+};
+
 struct riscv_isa_ext_data {
 	/* Name of the extension displayed to userspace via /proc/cpuinfo */
 	char uprop[RISCV_ISA_EXT_NAME_LEN_MAX];
@@ -62,6 +73,35 @@ struct riscv_isa_ext_data {
 	unsigned int isa_ext_id;
 };
 
+extern struct static_key_false riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_MAX];
+
+static __always_inline int riscv_isa_ext2key(int num)
+{
+	switch (num) {
+	case RISCV_ISA_EXT_f:
+		return RISCV_ISA_EXT_KEY_FPU;
+	case RISCV_ISA_EXT_d:
+		return RISCV_ISA_EXT_KEY_FPU;
+	default:
+		return -EINVAL;
+	}
+}
+
+/*
+ * @num must be a compile-time constant.
+ */
+static __always_inline bool riscv_isa_have_key_extension(int num)
+{
+	if (RISCV_ISA_EXT_ID_MAX <= num)
+		return false;
+
+	num = riscv_isa_ext2key(num);
+	if (RISCV_ISA_EXT_KEY_MAX <= num || num < 0)
+		return false;
+
+	return static_branch_likely(&riscv_isa_ext_keys[num]);
+}
+
 unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap);
 
 #define riscv_isa_extension_mask(ext) BIT_MASK(RISCV_ISA_EXT_##ext)
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 1b2d42d7f589..89f886b35357 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -24,6 +24,8 @@ static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
 #ifdef CONFIG_FPU
 __ro_after_init DEFINE_STATIC_KEY_FALSE(cpu_hwcap_fpu);
 #endif
+__ro_after_init DEFINE_STATIC_KEY_ARRAY_FALSE(riscv_isa_ext_keys, RISCV_ISA_EXT_KEY_MAX);
+EXPORT_SYMBOL(riscv_isa_ext_keys);
 
 /**
  * riscv_isa_extension_base() - Get base extension word
@@ -232,6 +234,11 @@ void __init riscv_fill_hwcap(void)
 			print_str[j++] = (char)('a' + i);
 	pr_info("riscv: ELF capabilities %s\n", print_str);
 
+	for_each_set_bit(i, riscv_isa, RISCV_ISA_EXT_MAX) {
+		j = riscv_isa_ext2key(i);
+		if (j >= 0)
+			static_branch_enable(&riscv_isa_ext_keys[j]);
+	}
 #ifdef CONFIG_FPU
 	if (elf_hwcap & (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D))
 		static_branch_enable(&cpu_hwcap_fpu);
-- 
2.34.1


_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

[PATCH 2/2] riscv: switch has_fpu() to the unified static key mechanism

[Jisheng Zhang]

This is to use the unified static key mechanism instead of putting
static key related here and there.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 arch/riscv/include/asm/switch_to.h | 5 +++--
 arch/riscv/kernel/cpufeature.c     | 7 -------
 2 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
index 0a3f4f95c555..3f407182080d 100644
--- a/arch/riscv/include/asm/switch_to.h
+++ b/arch/riscv/include/asm/switch_to.h
@@ -8,6 +8,7 @@
 
 #include <linux/jump_label.h>
 #include <linux/sched/task_stack.h>
+#include <asm/hwcap.h>
 #include <asm/processor.h>
 #include <asm/ptrace.h>
 #include <asm/csr.h>
@@ -56,10 +57,10 @@ static inline void __switch_to_aux(struct task_struct *prev,
 	fstate_restore(next, task_pt_regs(next));
 }
 
-extern struct static_key_false cpu_hwcap_fpu;
 static __always_inline bool has_fpu(void)
 {
-	return static_branch_likely(&cpu_hwcap_fpu);
+	return riscv_isa_have_key_extension(RISCV_ISA_EXT_d) ||
+		riscv_isa_have_key_extension(RISCV_ISA_EXT_f);
 }
 #else
 static __always_inline bool has_fpu(void) { return false; }
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 89f886b35357..0235391be84b 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -21,9 +21,6 @@ unsigned long elf_hwcap __read_mostly;
 /* Host ISA bitmap */
 static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
 
-#ifdef CONFIG_FPU
-__ro_after_init DEFINE_STATIC_KEY_FALSE(cpu_hwcap_fpu);
-#endif
 __ro_after_init DEFINE_STATIC_KEY_ARRAY_FALSE(riscv_isa_ext_keys, RISCV_ISA_EXT_KEY_MAX);
 EXPORT_SYMBOL(riscv_isa_ext_keys);
 
@@ -239,8 +236,4 @@ void __init riscv_fill_hwcap(void)
 		if (j >= 0)
 			static_branch_enable(&riscv_isa_ext_keys[j]);
 	}
-#ifdef CONFIG_FPU
-	if (elf_hwcap & (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D))
-		static_branch_enable(&cpu_hwcap_fpu);
-#endif
 }
-- 
2.34.1


_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

Re: [PATCH 1/2] riscv: introduce unified static key mechanism for ISA extensions

[Atish Patra]

On Tue, May 17, 2022 at 11:53 AM Jisheng Zhang <jszhang@kernel.org> wrote:
>
> Currently, riscv has several extensions which may not be supported on
> all riscv platforms, for example, FPU and so on. To support unified
> kernel Image style, we need to check whether the feature is supported

/s/suportted/supported


> or not. If the check sits at hot code path, then performance will be
> impacted a lot. static key can be used to solve the issue. In the past
> FPU support has been converted to use static key mechanism. I believe
> we will have similar cases in the future.
>
> this patch tries to add an unified mechanism to use static keys for
> some ISA extensions by implementing an array of default-false static keys
> and enabling them when detected.
>
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> ---
>  arch/riscv/include/asm/hwcap.h | 40 ++++++++++++++++++++++++++++++++++
>  arch/riscv/kernel/cpufeature.c |  7 ++++++
>  2 files changed, 47 insertions(+)
>
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index 0734e42f74f2..b0433d2b880d 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -12,6 +12,7 @@
>  #include <uapi/asm/hwcap.h>
>
>  #ifndef __ASSEMBLY__
> +#include <linux/jump_label.h>
>  /*
>   * This yields a mask that user programs can use to figure out what
>   * instruction set this cpu supports.
> @@ -55,6 +56,16 @@ enum riscv_isa_ext_id {
>         RISCV_ISA_EXT_ID_MAX = RISCV_ISA_EXT_MAX,
>  };
>
> +/*
> + * This enum represents the logical ID for each RISC-V ISA extension static
> + * keys. We can use static key to optimize code path if some ISA extensions
> + * are available.
> + */
> +enum riscv_isa_ext_key {
> +       RISCV_ISA_EXT_KEY_FPU,          /* For 'F' and 'D' */
> +       RISCV_ISA_EXT_KEY_MAX,
> +};
> +
>  struct riscv_isa_ext_data {
>         /* Name of the extension displayed to userspace via /proc/cpuinfo */
>         char uprop[RISCV_ISA_EXT_NAME_LEN_MAX];
> @@ -62,6 +73,35 @@ struct riscv_isa_ext_data {
>         unsigned int isa_ext_id;
>  };
>
> +extern struct static_key_false riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_MAX];
> +
> +static __always_inline int riscv_isa_ext2key(int num)
> +{
> +       switch (num) {
> +       case RISCV_ISA_EXT_f:
> +               return RISCV_ISA_EXT_KEY_FPU;
> +       case RISCV_ISA_EXT_d:
> +               return RISCV_ISA_EXT_KEY_FPU;
> +       default:
> +               return -EINVAL;
> +       }
> +}
> +
> +/*
> + * @num must be a compile-time constant.
> + */
> +static __always_inline bool riscv_isa_have_key_extension(int num)
> +{
> +       if (RISCV_ISA_EXT_ID_MAX <= num)
> +               return false;
> +
> +       num = riscv_isa_ext2key(num);
 > +       if (RISCV_ISA_EXT_KEY_MAX <= num || num < 0)
> +               return false;
> +

Why do you need the additional check in the hot path ?
riscv_isa_ext_keys array can be directly accessed at the caller
instead of calling this function.

> +       return static_branch_likely(&riscv_isa_ext_keys[num]);
> +}
> +



>  unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap);
>
>  #define riscv_isa_extension_mask(ext) BIT_MASK(RISCV_ISA_EXT_##ext)
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 1b2d42d7f589..89f886b35357 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -24,6 +24,8 @@ static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
>  #ifdef CONFIG_FPU
>  __ro_after_init DEFINE_STATIC_KEY_FALSE(cpu_hwcap_fpu);
>  #endif
> +__ro_after_init DEFINE_STATIC_KEY_ARRAY_FALSE(riscv_isa_ext_keys, RISCV_ISA_EXT_KEY_MAX);
> +EXPORT_SYMBOL(riscv_isa_ext_keys);
>
>  /**
>   * riscv_isa_extension_base() - Get base extension word
> @@ -232,6 +234,11 @@ void __init riscv_fill_hwcap(void)
>                         print_str[j++] = (char)('a' + i);
>         pr_info("riscv: ELF capabilities %s\n", print_str);
>
> +       for_each_set_bit(i, riscv_isa, RISCV_ISA_EXT_MAX) {
> +               j = riscv_isa_ext2key(i);
> +               if (j >= 0)
> +                       static_branch_enable(&riscv_isa_ext_keys[j]);
> +       }
>  #ifdef CONFIG_FPU
>         if (elf_hwcap & (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D))
>                 static_branch_enable(&cpu_hwcap_fpu);
> --
> 2.34.1
>


--
Regards,
Atish

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

Re: [PATCH 1/2] riscv: introduce unified static key mechanism for ISA extensions

[Jisheng Zhang]

On Sun, May 22, 2022 at 12:33:12AM -0700, Atish Patra wrote:
> On Tue, May 17, 2022 at 11:53 AM Jisheng Zhang <jszhang@kernel.org> wrote:
> >
> > Currently, riscv has several extensions which may not be supported on
> > all riscv platforms, for example, FPU and so on. To support unified
> > kernel Image style, we need to check whether the feature is supported
> 
> /s/suportted/supported

Thanks, will fix it in v2 soon.
> 
> > or not. If the check sits at hot code path, then performance will be
> > impacted a lot. static key can be used to solve the issue. In the past
> > FPU support has been converted to use static key mechanism. I believe
> > we will have similar cases in the future.
> >
> > this patch tries to add an unified mechanism to use static keys for
> > some ISA extensions by implementing an array of default-false static keys
> > and enabling them when detected.
> >
> > Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> > ---
> >  arch/riscv/include/asm/hwcap.h | 40 ++++++++++++++++++++++++++++++++++
> >  arch/riscv/kernel/cpufeature.c |  7 ++++++
> >  2 files changed, 47 insertions(+)
> >
> > diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> > index 0734e42f74f2..b0433d2b880d 100644
> > --- a/arch/riscv/include/asm/hwcap.h
> > +++ b/arch/riscv/include/asm/hwcap.h
> > @@ -12,6 +12,7 @@
> >  #include <uapi/asm/hwcap.h>
> >
> >  #ifndef __ASSEMBLY__
> > +#include <linux/jump_label.h>
> >  /*
> >   * This yields a mask that user programs can use to figure out what
> >   * instruction set this cpu supports.
> > @@ -55,6 +56,16 @@ enum riscv_isa_ext_id {
> >         RISCV_ISA_EXT_ID_MAX = RISCV_ISA_EXT_MAX,
> >  };
> >
> > +/*
> > + * This enum represents the logical ID for each RISC-V ISA extension static
> > + * keys. We can use static key to optimize code path if some ISA extensions
> > + * are available.
> > + */
> > +enum riscv_isa_ext_key {
> > +       RISCV_ISA_EXT_KEY_FPU,          /* For 'F' and 'D' */
> > +       RISCV_ISA_EXT_KEY_MAX,
> > +};
> > +
> >  struct riscv_isa_ext_data {
> >         /* Name of the extension displayed to userspace via /proc/cpuinfo */
> >         char uprop[RISCV_ISA_EXT_NAME_LEN_MAX];
> > @@ -62,6 +73,35 @@ struct riscv_isa_ext_data {
> >         unsigned int isa_ext_id;
> >  };
> >
> > +extern struct static_key_false riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_MAX];
> > +
> > +static __always_inline int riscv_isa_ext2key(int num)
> > +{
> > +       switch (num) {
> > +       case RISCV_ISA_EXT_f:
> > +               return RISCV_ISA_EXT_KEY_FPU;
> > +       case RISCV_ISA_EXT_d:
> > +               return RISCV_ISA_EXT_KEY_FPU;
> > +       default:
> > +               return -EINVAL;
> > +       }
> > +}
> > +
> > +/*
> > + * @num must be a compile-time constant.
> > + */
> > +static __always_inline bool riscv_isa_have_key_extension(int num)
> > +{
> > +       if (RISCV_ISA_EXT_ID_MAX <= num)
> > +               return false;
> > +
> > +       num = riscv_isa_ext2key(num);
>  > +       if (RISCV_ISA_EXT_KEY_MAX <= num || num < 0)
> > +               return false;
> > +
> 
> Why do you need the additional check in the hot path ?
> riscv_isa_ext_keys array can be directly accessed at the caller
> instead of calling this function.

directly accessing the keys can make the code simpler, thanks for
the hint.

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv