[PATCH v2 0/2] introduce unified static key mechanism for ISA ext

[PATCH v2 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 supported 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.

Since v1:
  - fix typo, thank Atish
  - remove riscv_isa_have_key_extension() instead use the isa ext keys
    directly as pointed out by Atish.

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     | 25 +++++++++++++++++++++++++
 arch/riscv/include/asm/switch_to.h |  4 ++--
 arch/riscv/kernel/cpufeature.c     | 14 +++++++-------
 3 files changed, 34 insertions(+), 9 deletions(-)

-- 
2.34.1

[PATCH v2 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 supported 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.

Since v1:
  - fix typo, thank Atish
  - remove riscv_isa_have_key_extension() instead use the isa ext keys
    directly as pointed out by Atish.

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     | 25 +++++++++++++++++++++++++
 arch/riscv/include/asm/switch_to.h |  4 ++--
 arch/riscv/kernel/cpufeature.c     | 14 +++++++-------
 3 files changed, 34 insertions(+), 9 deletions(-)

-- 
2.34.1


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[PATCH v2 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 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 | 25 +++++++++++++++++++++++++
 arch/riscv/kernel/cpufeature.c |  7 +++++++
 2 files changed, 32 insertions(+)

diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index 0734e42f74f2..d3e113fe7366 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 +73,20 @@ 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;
+	}
+}
+
 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

[PATCH v2 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 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 | 25 +++++++++++++++++++++++++
 arch/riscv/kernel/cpufeature.c |  7 +++++++
 2 files changed, 32 insertions(+)

diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index 0734e42f74f2..d3e113fe7366 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 +73,20 @@ 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;
+	}
+}
+
 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 v2 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 | 4 ++--
 arch/riscv/kernel/cpufeature.c     | 7 -------
 2 files changed, 2 insertions(+), 9 deletions(-)

diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
index 0a3f4f95c555..11463489fec6 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 +57,9 @@ 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 static_branch_likely(&riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_FPU]);
 }
 #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

[PATCH v2 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 | 4 ++--
 arch/riscv/kernel/cpufeature.c     | 7 -------
 2 files changed, 2 insertions(+), 9 deletions(-)

diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
index 0a3f4f95c555..11463489fec6 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 +57,9 @@ 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 static_branch_likely(&riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_FPU]);
 }
 #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


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http://lists.infradead.org/mailman/listinfo/linux-riscv

Re: [PATCH v2 2/2] riscv: switch has_fpu() to the unified static key mechanism

[Atish Patra]

On Sun, May 22, 2022 at 8:44 AM Jisheng Zhang <jszhang@kernel.org> wrote:
>
> 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 | 4 ++--
>  arch/riscv/kernel/cpufeature.c     | 7 -------
>  2 files changed, 2 insertions(+), 9 deletions(-)
>
> diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
> index 0a3f4f95c555..11463489fec6 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 +57,9 @@ 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 static_branch_likely(&riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_FPU]);
>  }
>  #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
>

Reviewed-by: Atish Patra <atishp@rivosinc.com>

-- 
Regards,
Atish

Re: [PATCH v2 2/2] riscv: switch has_fpu() to the unified static key mechanism

[Atish Patra]

On Sun, May 22, 2022 at 8:44 AM Jisheng Zhang <jszhang@kernel.org> wrote:
>
> 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 | 4 ++--
>  arch/riscv/kernel/cpufeature.c     | 7 -------
>  2 files changed, 2 insertions(+), 9 deletions(-)
>
> diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
> index 0a3f4f95c555..11463489fec6 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 +57,9 @@ 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 static_branch_likely(&riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_FPU]);
>  }
>  #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
>

Reviewed-by: Atish Patra <atishp@rivosinc.com>

-- 
Regards,
Atish

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

Re: [PATCH v2 1/2] riscv: introduce unified static key mechanism for ISA extensions

[Atish Patra]

On Sun, May 22, 2022 at 8:44 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
> 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 | 25 +++++++++++++++++++++++++
>  arch/riscv/kernel/cpufeature.c |  7 +++++++
>  2 files changed, 32 insertions(+)
>
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index 0734e42f74f2..d3e113fe7366 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 +73,20 @@ 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;
> +       }
> +}
> +
>  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
>


Reviewed-by: Atish Patra <atishp@rivosinc.com>
-- 
Regards,
Atish

Re: [PATCH v2 1/2] riscv: introduce unified static key mechanism for ISA extensions

[Atish Patra]

On Sun, May 22, 2022 at 8:44 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
> 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 | 25 +++++++++++++++++++++++++
>  arch/riscv/kernel/cpufeature.c |  7 +++++++
>  2 files changed, 32 insertions(+)
>
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index 0734e42f74f2..d3e113fe7366 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 +73,20 @@ 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;
> +       }
> +}
> +
>  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
>


Reviewed-by: Atish Patra <atishp@rivosinc.com>
-- 
Regards,
Atish

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

Re: [PATCH v2 1/2] riscv: introduce unified static key mechanism for ISA extensions

[Anup Patel]

On Sun, May 22, 2022 at 9:14 PM 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
> 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>

Looks good to me.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup

> ---
>  arch/riscv/include/asm/hwcap.h | 25 +++++++++++++++++++++++++
>  arch/riscv/kernel/cpufeature.c |  7 +++++++
>  2 files changed, 32 insertions(+)
>
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index 0734e42f74f2..d3e113fe7366 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 +73,20 @@ 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;
> +       }
> +}
> +
>  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
>

Re: [PATCH v2 1/2] riscv: introduce unified static key mechanism for ISA extensions

[Anup Patel]

On Sun, May 22, 2022 at 9:14 PM 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
> 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>

Looks good to me.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup

> ---
>  arch/riscv/include/asm/hwcap.h | 25 +++++++++++++++++++++++++
>  arch/riscv/kernel/cpufeature.c |  7 +++++++
>  2 files changed, 32 insertions(+)
>
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index 0734e42f74f2..d3e113fe7366 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 +73,20 @@ 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;
> +       }
> +}
> +
>  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
>

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Re: [PATCH v2 2/2] riscv: switch has_fpu() to the unified static key mechanism

[Anup Patel]

On Sun, May 22, 2022 at 9:14 PM Jisheng Zhang <jszhang@kernel.org> wrote:
>
> 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>

Looks good to me.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup

> ---
>  arch/riscv/include/asm/switch_to.h | 4 ++--
>  arch/riscv/kernel/cpufeature.c     | 7 -------
>  2 files changed, 2 insertions(+), 9 deletions(-)
>
> diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
> index 0a3f4f95c555..11463489fec6 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 +57,9 @@ 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 static_branch_likely(&riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_FPU]);
>  }
>  #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
>

Re: [PATCH v2 2/2] riscv: switch has_fpu() to the unified static key mechanism

[Anup Patel]

On Sun, May 22, 2022 at 9:14 PM Jisheng Zhang <jszhang@kernel.org> wrote:
>
> 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>

Looks good to me.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup

> ---
>  arch/riscv/include/asm/switch_to.h | 4 ++--
>  arch/riscv/kernel/cpufeature.c     | 7 -------
>  2 files changed, 2 insertions(+), 9 deletions(-)
>
> diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
> index 0a3f4f95c555..11463489fec6 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 +57,9 @@ 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 static_branch_likely(&riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_FPU]);
>  }
>  #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
>

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Re: [PATCH v2 0/2] introduce unified static key mechanism for ISA ext

[Palmer Dabbelt]

On Sun, 22 May 2022 08:35:41 PDT (-0700), 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 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.
>
> Since v1:
>   - fix typo, thank Atish
>   - remove riscv_isa_have_key_extension() instead use the isa ext keys
>     directly as pointed out by Atish.
>
> 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     | 25 +++++++++++++++++++++++++
>  arch/riscv/include/asm/switch_to.h |  4 ++--
>  arch/riscv/kernel/cpufeature.c     | 14 +++++++-------
>  3 files changed, 34 insertions(+), 9 deletions(-)

Thanks, this is on for-next.

Re: [PATCH v2 0/2] introduce unified static key mechanism for ISA ext

[Palmer Dabbelt]

On Sun, 22 May 2022 08:35:41 PDT (-0700), 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 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.
>
> Since v1:
>   - fix typo, thank Atish
>   - remove riscv_isa_have_key_extension() instead use the isa ext keys
>     directly as pointed out by Atish.
>
> 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     | 25 +++++++++++++++++++++++++
>  arch/riscv/include/asm/switch_to.h |  4 ++--
>  arch/riscv/kernel/cpufeature.c     | 14 +++++++-------
>  3 files changed, 34 insertions(+), 9 deletions(-)

Thanks, this is on for-next.

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