* [PATCH v3 0/2] riscv: Optimize bitops with Zbb extension
@ 2023-09-26 9:46 Xiao Wang
2023-09-26 9:46 ` [PATCH v3 1/2] riscv: Rearrange hwcap.h and cpufeature.h Xiao Wang
2023-09-26 9:46 ` [PATCH v3 2/2] riscv: Optimize bitops with Zbb extension Xiao Wang
0 siblings, 2 replies; 5+ messages in thread
From: Xiao Wang @ 2023-09-26 9:46 UTC (permalink / raw)
To: paul.walmsley, palmer, aou, ardb
Cc: anup, haicheng.li, ajones, yujie.liu, linux-riscv, linux-efi,
linux-kernel, Xiao Wang
Bitops optimization with specialized instructions is common practice in
popular ISAs, this patch set uses RISC-V Zbb extension to optimize four
bitops: __ffs, __fls, ffs and fls.
The first patch rearranges the content in hwcap.h cpufeature.h, it helps
to avoid a cyclic header including issue for patch 2.
The second patch leverages the alternative mechanism to dynamically apply
this optimization.
The series has following dependency:
https://lore.kernel.org/linux-riscv/20230918131518.56803-8-ajones@ventanamicro.com/
Thanks,
Xiao
v3:
- Fix riscv32 build issue reported by kernel test robot. V3 changes "hwcap.h" to
"cpufeature.h" for files where cpu feature detection APIs are used. (Yujie)
v2:
- Remove the "EFI_" prefix from macro name "EFI_NO_ALTERNATIVE" to make it
generic. (Ard)
- patch-1 is added, it's based on "RISC-V: Enable cbo.zero in usermode". (Andrew)
Xiao Wang (2):
riscv: Rearrange hwcap.h and cpufeature.h
riscv: Optimize bitops with Zbb extension
arch/riscv/include/asm/bitops.h | 266 +++++++++++++++++++++++++-
arch/riscv/include/asm/cpufeature.h | 83 ++++++++
arch/riscv/include/asm/elf.h | 2 +-
arch/riscv/include/asm/hwcap.h | 91 ---------
arch/riscv/include/asm/pgtable.h | 1 +
arch/riscv/include/asm/switch_to.h | 2 +-
arch/riscv/include/asm/vector.h | 2 +-
arch/riscv/kvm/aia.c | 2 +-
arch/riscv/kvm/main.c | 2 +-
arch/riscv/kvm/tlb.c | 2 +-
arch/riscv/kvm/vcpu_fp.c | 2 +-
arch/riscv/kvm/vcpu_onereg.c | 2 +-
arch/riscv/kvm/vcpu_vector.c | 2 +-
drivers/clocksource/timer-riscv.c | 2 +-
drivers/firmware/efi/libstub/Makefile | 2 +-
drivers/perf/riscv_pmu_sbi.c | 2 +-
16 files changed, 359 insertions(+), 106 deletions(-)
--
2.25.1
_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH v3 1/2] riscv: Rearrange hwcap.h and cpufeature.h
2023-09-26 9:46 [PATCH v3 0/2] riscv: Optimize bitops with Zbb extension Xiao Wang
@ 2023-09-26 9:46 ` Xiao Wang
2023-09-26 9:46 ` [PATCH v3 2/2] riscv: Optimize bitops with Zbb extension Xiao Wang
1 sibling, 0 replies; 5+ messages in thread
From: Xiao Wang @ 2023-09-26 9:46 UTC (permalink / raw)
To: paul.walmsley, palmer, aou, ardb
Cc: anup, haicheng.li, ajones, yujie.liu, linux-riscv, linux-efi,
linux-kernel, Xiao Wang
Now hwcap.h and cpufeature.h are mutually including each other, and most of
the variable/API declarations in hwcap.h are implemented in cpufeature.c,
so, it's better to move them into cpufeature.h and leave only macros for
ISA extension logical IDs in hwcap.h.
BTW, the riscv_isa_extension_mask macro is not used now, so this patch
removes it.
Suggested-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Xiao Wang <xiao.w.wang@intel.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
---
arch/riscv/include/asm/cpufeature.h | 83 ++++++++++++++++++++++++++
arch/riscv/include/asm/elf.h | 2 +-
arch/riscv/include/asm/hwcap.h | 91 -----------------------------
arch/riscv/include/asm/pgtable.h | 1 +
arch/riscv/include/asm/switch_to.h | 2 +-
arch/riscv/include/asm/vector.h | 2 +-
arch/riscv/kvm/aia.c | 2 +-
arch/riscv/kvm/main.c | 2 +-
arch/riscv/kvm/tlb.c | 2 +-
arch/riscv/kvm/vcpu_fp.c | 2 +-
arch/riscv/kvm/vcpu_onereg.c | 2 +-
arch/riscv/kvm/vcpu_vector.c | 2 +-
drivers/clocksource/timer-riscv.c | 2 +-
drivers/perf/riscv_pmu_sbi.c | 2 +-
14 files changed, 95 insertions(+), 102 deletions(-)
diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index 13b7d35648a9..3061d33abc2f 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -7,7 +7,10 @@
#define _ASM_CPUFEATURE_H
#include <linux/bitmap.h>
+#include <linux/jump_label.h>
#include <asm/hwcap.h>
+#include <asm/alternative-macros.h>
+#include <asm/errno.h>
/*
* These are probed via a device_initcall(), via either the SBI or directly
@@ -33,4 +36,84 @@ extern struct riscv_isainfo hart_isa[NR_CPUS];
void check_unaligned_access(int cpu);
void riscv_user_isa_enable(void);
+unsigned long riscv_get_elf_hwcap(void);
+
+struct riscv_isa_ext_data {
+ const unsigned int id;
+ const char *name;
+ const char *property;
+};
+
+extern const struct riscv_isa_ext_data riscv_isa_ext[];
+extern const size_t riscv_isa_ext_count;
+extern bool riscv_isa_fallback;
+
+unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap);
+
+bool __riscv_isa_extension_available(const unsigned long *isa_bitmap, int bit);
+#define riscv_isa_extension_available(isa_bitmap, ext) \
+ __riscv_isa_extension_available(isa_bitmap, RISCV_ISA_EXT_##ext)
+
+static __always_inline bool
+riscv_has_extension_likely(const unsigned long ext)
+{
+ compiletime_assert(ext < RISCV_ISA_EXT_MAX,
+ "ext must be < RISCV_ISA_EXT_MAX");
+
+ if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
+ asm_volatile_goto(
+ ALTERNATIVE("j %l[l_no]", "nop", 0, %[ext], 1)
+ :
+ : [ext] "i" (ext)
+ :
+ : l_no);
+ } else {
+ if (!__riscv_isa_extension_available(NULL, ext))
+ goto l_no;
+ }
+
+ return true;
+l_no:
+ return false;
+}
+
+static __always_inline bool
+riscv_has_extension_unlikely(const unsigned long ext)
+{
+ compiletime_assert(ext < RISCV_ISA_EXT_MAX,
+ "ext must be < RISCV_ISA_EXT_MAX");
+
+ if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
+ asm_volatile_goto(
+ ALTERNATIVE("nop", "j %l[l_yes]", 0, %[ext], 1)
+ :
+ : [ext] "i" (ext)
+ :
+ : l_yes);
+ } else {
+ if (__riscv_isa_extension_available(NULL, ext))
+ goto l_yes;
+ }
+
+ return false;
+l_yes:
+ return true;
+}
+
+static __always_inline bool riscv_cpu_has_extension_likely(int cpu, const unsigned long ext)
+{
+ if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) && riscv_has_extension_likely(ext))
+ return true;
+
+ return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
+}
+
+static __always_inline bool riscv_cpu_has_extension_unlikely(int cpu, const unsigned long ext)
+{
+ if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) && riscv_has_extension_unlikely(ext))
+ return true;
+
+ return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
+}
+
#endif
diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
index b3b2dfbdf945..06c236bfab53 100644
--- a/arch/riscv/include/asm/elf.h
+++ b/arch/riscv/include/asm/elf.h
@@ -14,7 +14,7 @@
#include <asm/auxvec.h>
#include <asm/byteorder.h>
#include <asm/cacheinfo.h>
-#include <asm/hwcap.h>
+#include <asm/cpufeature.h>
/*
* These are used to set parameters in the core dumps.
diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index 31774bcdf1c6..141b7109c25c 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -8,9 +8,6 @@
#ifndef _ASM_RISCV_HWCAP_H
#define _ASM_RISCV_HWCAP_H
-#include <asm/alternative-macros.h>
-#include <asm/errno.h>
-#include <linux/bits.h>
#include <uapi/asm/hwcap.h>
#define RISCV_ISA_EXT_a ('a' - 'a')
@@ -67,92 +64,4 @@
#define RISCV_ISA_EXT_SxAIA RISCV_ISA_EXT_SSAIA
#endif
-#ifndef __ASSEMBLY__
-
-#include <linux/jump_label.h>
-#include <asm/cpufeature.h>
-
-unsigned long riscv_get_elf_hwcap(void);
-
-struct riscv_isa_ext_data {
- const unsigned int id;
- const char *name;
- const char *property;
-};
-
-extern const struct riscv_isa_ext_data riscv_isa_ext[];
-extern const size_t riscv_isa_ext_count;
-extern bool riscv_isa_fallback;
-
-unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap);
-
-#define riscv_isa_extension_mask(ext) BIT_MASK(RISCV_ISA_EXT_##ext)
-
-bool __riscv_isa_extension_available(const unsigned long *isa_bitmap, int bit);
-#define riscv_isa_extension_available(isa_bitmap, ext) \
- __riscv_isa_extension_available(isa_bitmap, RISCV_ISA_EXT_##ext)
-
-static __always_inline bool
-riscv_has_extension_likely(const unsigned long ext)
-{
- compiletime_assert(ext < RISCV_ISA_EXT_MAX,
- "ext must be < RISCV_ISA_EXT_MAX");
-
- if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
- asm_volatile_goto(
- ALTERNATIVE("j %l[l_no]", "nop", 0, %[ext], 1)
- :
- : [ext] "i" (ext)
- :
- : l_no);
- } else {
- if (!__riscv_isa_extension_available(NULL, ext))
- goto l_no;
- }
-
- return true;
-l_no:
- return false;
-}
-
-static __always_inline bool
-riscv_has_extension_unlikely(const unsigned long ext)
-{
- compiletime_assert(ext < RISCV_ISA_EXT_MAX,
- "ext must be < RISCV_ISA_EXT_MAX");
-
- if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
- asm_volatile_goto(
- ALTERNATIVE("nop", "j %l[l_yes]", 0, %[ext], 1)
- :
- : [ext] "i" (ext)
- :
- : l_yes);
- } else {
- if (__riscv_isa_extension_available(NULL, ext))
- goto l_yes;
- }
-
- return false;
-l_yes:
- return true;
-}
-
-static __always_inline bool riscv_cpu_has_extension_likely(int cpu, const unsigned long ext)
-{
- if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) && riscv_has_extension_likely(ext))
- return true;
-
- return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
-}
-
-static __always_inline bool riscv_cpu_has_extension_unlikely(int cpu, const unsigned long ext)
-{
- if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE) && riscv_has_extension_unlikely(ext))
- return true;
-
- return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
-}
-#endif
-
#endif /* _ASM_RISCV_HWCAP_H */
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index b2ba3f79cfe9..e05b5dc1f0cb 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -291,6 +291,7 @@ static inline pte_t pud_pte(pud_t pud)
}
#ifdef CONFIG_RISCV_ISA_SVNAPOT
+#include <asm/cpufeature.h>
static __always_inline bool has_svnapot(void)
{
diff --git a/arch/riscv/include/asm/switch_to.h b/arch/riscv/include/asm/switch_to.h
index a727be723c56..f90d8e42f3c7 100644
--- a/arch/riscv/include/asm/switch_to.h
+++ b/arch/riscv/include/asm/switch_to.h
@@ -9,7 +9,7 @@
#include <linux/jump_label.h>
#include <linux/sched/task_stack.h>
#include <asm/vector.h>
-#include <asm/hwcap.h>
+#include <asm/cpufeature.h>
#include <asm/processor.h>
#include <asm/ptrace.h>
#include <asm/csr.h>
diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
index c5ee07b3df07..87aaef656257 100644
--- a/arch/riscv/include/asm/vector.h
+++ b/arch/riscv/include/asm/vector.h
@@ -15,7 +15,7 @@
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <asm/ptrace.h>
-#include <asm/hwcap.h>
+#include <asm/cpufeature.h>
#include <asm/csr.h>
#include <asm/asm.h>
diff --git a/arch/riscv/kvm/aia.c b/arch/riscv/kvm/aia.c
index 74bb27440527..a944294f6f23 100644
--- a/arch/riscv/kvm/aia.c
+++ b/arch/riscv/kvm/aia.c
@@ -14,7 +14,7 @@
#include <linux/kvm_host.h>
#include <linux/percpu.h>
#include <linux/spinlock.h>
-#include <asm/hwcap.h>
+#include <asm/cpufeature.h>
#include <asm/kvm_aia_imsic.h>
struct aia_hgei_control {
diff --git a/arch/riscv/kvm/main.c b/arch/riscv/kvm/main.c
index 48ae0d4b3932..225a435d9c9a 100644
--- a/arch/riscv/kvm/main.c
+++ b/arch/riscv/kvm/main.c
@@ -11,7 +11,7 @@
#include <linux/module.h>
#include <linux/kvm_host.h>
#include <asm/csr.h>
-#include <asm/hwcap.h>
+#include <asm/cpufeature.h>
#include <asm/sbi.h>
long kvm_arch_dev_ioctl(struct file *filp,
diff --git a/arch/riscv/kvm/tlb.c b/arch/riscv/kvm/tlb.c
index 44bc324aeeb0..23c0e82b5103 100644
--- a/arch/riscv/kvm/tlb.c
+++ b/arch/riscv/kvm/tlb.c
@@ -12,7 +12,7 @@
#include <linux/kvm_host.h>
#include <asm/cacheflush.h>
#include <asm/csr.h>
-#include <asm/hwcap.h>
+#include <asm/cpufeature.h>
#include <asm/insn-def.h>
#define has_svinval() riscv_has_extension_unlikely(RISCV_ISA_EXT_SVINVAL)
diff --git a/arch/riscv/kvm/vcpu_fp.c b/arch/riscv/kvm/vcpu_fp.c
index 08ba48a395aa..030904d82b58 100644
--- a/arch/riscv/kvm/vcpu_fp.c
+++ b/arch/riscv/kvm/vcpu_fp.c
@@ -11,7 +11,7 @@
#include <linux/err.h>
#include <linux/kvm_host.h>
#include <linux/uaccess.h>
-#include <asm/hwcap.h>
+#include <asm/cpufeature.h>
#ifdef CONFIG_FPU
void kvm_riscv_vcpu_fp_reset(struct kvm_vcpu *vcpu)
diff --git a/arch/riscv/kvm/vcpu_onereg.c b/arch/riscv/kvm/vcpu_onereg.c
index 1b7e9fa265cb..b03e0c879dab 100644
--- a/arch/riscv/kvm/vcpu_onereg.c
+++ b/arch/riscv/kvm/vcpu_onereg.c
@@ -13,7 +13,7 @@
#include <linux/uaccess.h>
#include <linux/kvm_host.h>
#include <asm/cacheflush.h>
-#include <asm/hwcap.h>
+#include <asm/cpufeature.h>
#include <asm/kvm_vcpu_vector.h>
#include <asm/vector.h>
diff --git a/arch/riscv/kvm/vcpu_vector.c b/arch/riscv/kvm/vcpu_vector.c
index b430cbb69521..b339a2682f25 100644
--- a/arch/riscv/kvm/vcpu_vector.c
+++ b/arch/riscv/kvm/vcpu_vector.c
@@ -11,7 +11,7 @@
#include <linux/err.h>
#include <linux/kvm_host.h>
#include <linux/uaccess.h>
-#include <asm/hwcap.h>
+#include <asm/cpufeature.h>
#include <asm/kvm_vcpu_vector.h>
#include <asm/vector.h>
diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
index da3071b387eb..6d9e344e98f8 100644
--- a/drivers/clocksource/timer-riscv.c
+++ b/drivers/clocksource/timer-riscv.c
@@ -24,7 +24,7 @@
#include <linux/of_irq.h>
#include <clocksource/timer-riscv.h>
#include <asm/smp.h>
-#include <asm/hwcap.h>
+#include <asm/cpufeature.h>
#include <asm/sbi.h>
#include <asm/timex.h>
diff --git a/drivers/perf/riscv_pmu_sbi.c b/drivers/perf/riscv_pmu_sbi.c
index 9a51053b1f99..b97d3f1abcb1 100644
--- a/drivers/perf/riscv_pmu_sbi.c
+++ b/drivers/perf/riscv_pmu_sbi.c
@@ -22,7 +22,7 @@
#include <asm/errata_list.h>
#include <asm/sbi.h>
-#include <asm/hwcap.h>
+#include <asm/cpufeature.h>
#define SYSCTL_NO_USER_ACCESS 0
#define SYSCTL_USER_ACCESS 1
--
2.25.1
_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH v3 2/2] riscv: Optimize bitops with Zbb extension
2023-09-26 9:46 [PATCH v3 0/2] riscv: Optimize bitops with Zbb extension Xiao Wang
2023-09-26 9:46 ` [PATCH v3 1/2] riscv: Rearrange hwcap.h and cpufeature.h Xiao Wang
@ 2023-09-26 9:46 ` Xiao Wang
2023-10-27 6:24 ` Charlie Jenkins
1 sibling, 1 reply; 5+ messages in thread
From: Xiao Wang @ 2023-09-26 9:46 UTC (permalink / raw)
To: paul.walmsley, palmer, aou, ardb
Cc: anup, haicheng.li, ajones, yujie.liu, linux-riscv, linux-efi,
linux-kernel, Xiao Wang
This patch leverages the alternative mechanism to dynamically optimize
bitops (including __ffs, __fls, ffs, fls) with Zbb instructions. When
Zbb ext is not supported by the runtime CPU, legacy implementation is
used. If Zbb is supported, then the optimized variants will be selected
via alternative patching.
The legacy bitops support is taken from the generic C implementation as
fallback.
If the parameter is a build-time constant, we leverage compiler builtin to
calculate the result directly, this approach is inspired by x86 bitops
implementation.
EFI stub runs before the kernel, so alternative mechanism should not be
used there, this patch introduces a macro NO_ALTERNATIVE for this purpose.
Signed-off-by: Xiao Wang <xiao.w.wang@intel.com>
---
arch/riscv/include/asm/bitops.h | 266 +++++++++++++++++++++++++-
drivers/firmware/efi/libstub/Makefile | 2 +-
2 files changed, 264 insertions(+), 4 deletions(-)
diff --git a/arch/riscv/include/asm/bitops.h b/arch/riscv/include/asm/bitops.h
index 3540b690944b..c97e774cb647 100644
--- a/arch/riscv/include/asm/bitops.h
+++ b/arch/riscv/include/asm/bitops.h
@@ -15,13 +15,273 @@
#include <asm/barrier.h>
#include <asm/bitsperlong.h>
+#if !defined(CONFIG_RISCV_ISA_ZBB) || defined(NO_ALTERNATIVE)
#include <asm-generic/bitops/__ffs.h>
-#include <asm-generic/bitops/ffz.h>
-#include <asm-generic/bitops/fls.h>
#include <asm-generic/bitops/__fls.h>
+#include <asm-generic/bitops/ffs.h>
+#include <asm-generic/bitops/fls.h>
+
+#else
+#include <asm/alternative-macros.h>
+#include <asm/hwcap.h>
+
+#if (BITS_PER_LONG == 64)
+#define CTZW "ctzw "
+#define CLZW "clzw "
+#elif (BITS_PER_LONG == 32)
+#define CTZW "ctz "
+#define CLZW "clz "
+#else
+#error "Unexpected BITS_PER_LONG"
+#endif
+
+static __always_inline unsigned long variable__ffs(unsigned long word)
+{
+ int num;
+
+ asm_volatile_goto(
+ ALTERNATIVE("j %l[legacy]", "nop", 0, RISCV_ISA_EXT_ZBB, 1)
+ : : : : legacy);
+
+ asm volatile (
+ ".option push\n"
+ ".option arch,+zbb\n"
+ "ctz %0, %1\n"
+ ".option pop\n"
+ : "=r" (word) : "r" (word) :);
+
+ return word;
+
+legacy:
+ num = 0;
+#if BITS_PER_LONG == 64
+ if ((word & 0xffffffff) == 0) {
+ num += 32;
+ word >>= 32;
+ }
+#endif
+ if ((word & 0xffff) == 0) {
+ num += 16;
+ word >>= 16;
+ }
+ if ((word & 0xff) == 0) {
+ num += 8;
+ word >>= 8;
+ }
+ if ((word & 0xf) == 0) {
+ num += 4;
+ word >>= 4;
+ }
+ if ((word & 0x3) == 0) {
+ num += 2;
+ word >>= 2;
+ }
+ if ((word & 0x1) == 0)
+ num += 1;
+ return num;
+}
+
+/**
+ * __ffs - find first set bit in a long word
+ * @word: The word to search
+ *
+ * Undefined if no set bit exists, so code should check against 0 first.
+ */
+#define __ffs(word) \
+ (__builtin_constant_p(word) ? \
+ (unsigned long)__builtin_ctzl(word) : \
+ variable__ffs(word))
+
+static __always_inline unsigned long variable__fls(unsigned long word)
+{
+ int num;
+
+ asm_volatile_goto(
+ ALTERNATIVE("j %l[legacy]", "nop", 0, RISCV_ISA_EXT_ZBB, 1)
+ : : : : legacy);
+
+ asm volatile (
+ ".option push\n"
+ ".option arch,+zbb\n"
+ "clz %0, %1\n"
+ ".option pop\n"
+ : "=r" (word) : "r" (word) :);
+
+ return BITS_PER_LONG - 1 - word;
+
+legacy:
+ num = BITS_PER_LONG - 1;
+#if BITS_PER_LONG == 64
+ if (!(word & (~0ul << 32))) {
+ num -= 32;
+ word <<= 32;
+ }
+#endif
+ if (!(word & (~0ul << (BITS_PER_LONG-16)))) {
+ num -= 16;
+ word <<= 16;
+ }
+ if (!(word & (~0ul << (BITS_PER_LONG-8)))) {
+ num -= 8;
+ word <<= 8;
+ }
+ if (!(word & (~0ul << (BITS_PER_LONG-4)))) {
+ num -= 4;
+ word <<= 4;
+ }
+ if (!(word & (~0ul << (BITS_PER_LONG-2)))) {
+ num -= 2;
+ word <<= 2;
+ }
+ if (!(word & (~0ul << (BITS_PER_LONG-1))))
+ num -= 1;
+ return num;
+}
+
+/**
+ * __fls - find last set bit in a long word
+ * @word: the word to search
+ *
+ * Undefined if no set bit exists, so code should check against 0 first.
+ */
+#define __fls(word) \
+ (__builtin_constant_p(word) ? \
+ (unsigned long)(BITS_PER_LONG - 1 - __builtin_clzl(word)) : \
+ variable__fls(word))
+
+static __always_inline int variable_ffs(int x)
+{
+ int r;
+
+ asm_volatile_goto(
+ ALTERNATIVE("j %l[legacy]", "nop", 0, RISCV_ISA_EXT_ZBB, 1)
+ : : : : legacy);
+
+ asm volatile (
+ ".option push\n"
+ ".option arch,+zbb\n"
+ "bnez %1, 1f\n"
+ "li %0, 0\n"
+ "j 2f\n"
+ "1:\n"
+ CTZW "%0, %1\n"
+ "addi %0, %0, 1\n"
+ "2:\n"
+ ".option pop\n"
+ : "=r" (r) : "r" (x) :);
+
+ return r;
+
+legacy:
+ r = 1;
+ if (!x)
+ return 0;
+ if (!(x & 0xffff)) {
+ x >>= 16;
+ r += 16;
+ }
+ if (!(x & 0xff)) {
+ x >>= 8;
+ r += 8;
+ }
+ if (!(x & 0xf)) {
+ x >>= 4;
+ r += 4;
+ }
+ if (!(x & 3)) {
+ x >>= 2;
+ r += 2;
+ }
+ if (!(x & 1)) {
+ x >>= 1;
+ r += 1;
+ }
+ return r;
+}
+
+/**
+ * ffs - find first set bit in a word
+ * @x: the word to search
+ *
+ * This is defined the same way as the libc and compiler builtin ffs routines.
+ *
+ * ffs(value) returns 0 if value is 0 or the position of the first set bit if
+ * value is nonzero. The first (least significant) bit is at position 1.
+ */
+#define ffs(x) (__builtin_constant_p(x) ? __builtin_ffs(x) : variable_ffs(x))
+
+static __always_inline int variable_fls(unsigned int x)
+{
+ int r;
+
+ asm_volatile_goto(
+ ALTERNATIVE("j %l[legacy]", "nop", 0, RISCV_ISA_EXT_ZBB, 1)
+ : : : : legacy);
+
+ asm volatile (
+ ".option push\n"
+ ".option arch,+zbb\n"
+ "bnez %1, 1f\n"
+ "li %0, 0\n"
+ "j 2f\n"
+ "1:\n"
+ CLZW "%0, %1\n"
+ "neg %0, %0\n"
+ "addi %0, %0, 32\n"
+ "2:\n"
+ ".option pop\n"
+ : "=r" (r) : "r" (x) :);
+
+ return r;
+
+legacy:
+ r = 32;
+ if (!x)
+ return 0;
+ if (!(x & 0xffff0000u)) {
+ x <<= 16;
+ r -= 16;
+ }
+ if (!(x & 0xff000000u)) {
+ x <<= 8;
+ r -= 8;
+ }
+ if (!(x & 0xf0000000u)) {
+ x <<= 4;
+ r -= 4;
+ }
+ if (!(x & 0xc0000000u)) {
+ x <<= 2;
+ r -= 2;
+ }
+ if (!(x & 0x80000000u)) {
+ x <<= 1;
+ r -= 1;
+ }
+ return r;
+}
+
+/**
+ * fls - find last set bit in a word
+ * @x: the word to search
+ *
+ * This is defined in a similar way as ffs, but returns the position of the most
+ * significant set bit.
+ *
+ * fls(value) returns 0 if value is 0 or the position of the last set bit if
+ * value is nonzero. The last (most significant) bit is at position 32.
+ */
+#define fls(x) \
+ (__builtin_constant_p(x) ? \
+ (int)(((x) != 0) ? \
+ (sizeof(unsigned int) * 8 - __builtin_clz(x)) : 0) : \
+ variable_fls(x))
+
+#endif
+
+#include <asm-generic/bitops/ffz.h>
#include <asm-generic/bitops/fls64.h>
#include <asm-generic/bitops/sched.h>
-#include <asm-generic/bitops/ffs.h>
#include <asm-generic/bitops/hweight.h>
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index a1157c2a7170..d68cacd4e3af 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -28,7 +28,7 @@ cflags-$(CONFIG_ARM) += -DEFI_HAVE_STRLEN -DEFI_HAVE_STRNLEN \
-DEFI_HAVE_MEMCHR -DEFI_HAVE_STRRCHR \
-DEFI_HAVE_STRCMP -fno-builtin -fpic \
$(call cc-option,-mno-single-pic-base)
-cflags-$(CONFIG_RISCV) += -fpic
+cflags-$(CONFIG_RISCV) += -fpic -DNO_ALTERNATIVE
cflags-$(CONFIG_LOONGARCH) += -fpie
cflags-$(CONFIG_EFI_PARAMS_FROM_FDT) += -I$(srctree)/scripts/dtc/libfdt
--
2.25.1
_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v3 2/2] riscv: Optimize bitops with Zbb extension
2023-09-26 9:46 ` [PATCH v3 2/2] riscv: Optimize bitops with Zbb extension Xiao Wang
@ 2023-10-27 6:24 ` Charlie Jenkins
2023-10-30 2:12 ` Wang, Xiao W
0 siblings, 1 reply; 5+ messages in thread
From: Charlie Jenkins @ 2023-10-27 6:24 UTC (permalink / raw)
To: Xiao Wang
Cc: paul.walmsley, palmer, aou, ardb, anup, haicheng.li, ajones,
yujie.liu, linux-riscv, linux-efi, linux-kernel
On Tue, Sep 26, 2023 at 05:46:55PM +0800, Xiao Wang wrote:
> This patch leverages the alternative mechanism to dynamically optimize
> bitops (including __ffs, __fls, ffs, fls) with Zbb instructions. When
> Zbb ext is not supported by the runtime CPU, legacy implementation is
> used. If Zbb is supported, then the optimized variants will be selected
> via alternative patching.
>
> The legacy bitops support is taken from the generic C implementation as
> fallback.
>
> If the parameter is a build-time constant, we leverage compiler builtin to
> calculate the result directly, this approach is inspired by x86 bitops
> implementation.
>
> EFI stub runs before the kernel, so alternative mechanism should not be
> used there, this patch introduces a macro NO_ALTERNATIVE for this purpose.
>
> Signed-off-by: Xiao Wang <xiao.w.wang@intel.com>
> ---
> arch/riscv/include/asm/bitops.h | 266 +++++++++++++++++++++++++-
> drivers/firmware/efi/libstub/Makefile | 2 +-
> 2 files changed, 264 insertions(+), 4 deletions(-)
>
> diff --git a/arch/riscv/include/asm/bitops.h b/arch/riscv/include/asm/bitops.h
> index 3540b690944b..c97e774cb647 100644
> --- a/arch/riscv/include/asm/bitops.h
> +++ b/arch/riscv/include/asm/bitops.h
> @@ -15,13 +15,273 @@
> #include <asm/barrier.h>
> #include <asm/bitsperlong.h>
>
> +#if !defined(CONFIG_RISCV_ISA_ZBB) || defined(NO_ALTERNATIVE)
> #include <asm-generic/bitops/__ffs.h>
> -#include <asm-generic/bitops/ffz.h>
> -#include <asm-generic/bitops/fls.h>
> #include <asm-generic/bitops/__fls.h>
> +#include <asm-generic/bitops/ffs.h>
> +#include <asm-generic/bitops/fls.h>
> +
> +#else
> +#include <asm/alternative-macros.h>
> +#include <asm/hwcap.h>
> +
> +#if (BITS_PER_LONG == 64)
> +#define CTZW "ctzw "
> +#define CLZW "clzw "
> +#elif (BITS_PER_LONG == 32)
> +#define CTZW "ctz "
> +#define CLZW "clz "
> +#else
> +#error "Unexpected BITS_PER_LONG"
> +#endif
> +
> +static __always_inline unsigned long variable__ffs(unsigned long word)
> +{
> + int num;
> +
> + asm_volatile_goto(
> + ALTERNATIVE("j %l[legacy]", "nop", 0, RISCV_ISA_EXT_ZBB, 1)
> + : : : : legacy);
> +
> + asm volatile (
> + ".option push\n"
> + ".option arch,+zbb\n"
> + "ctz %0, %1\n"
> + ".option pop\n"
> + : "=r" (word) : "r" (word) :);
> +
> + return word;
That's so clean!
> +
> +legacy:
> + num = 0;
> +#if BITS_PER_LONG == 64
> + if ((word & 0xffffffff) == 0) {
> + num += 32;
> + word >>= 32;
> + }
> +#endif
> + if ((word & 0xffff) == 0) {
> + num += 16;
> + word >>= 16;
> + }
> + if ((word & 0xff) == 0) {
> + num += 8;
> + word >>= 8;
> + }
> + if ((word & 0xf) == 0) {
> + num += 4;
> + word >>= 4;
> + }
> + if ((word & 0x3) == 0) {
> + num += 2;
> + word >>= 2;
> + }
> + if ((word & 0x1) == 0)
> + num += 1;
> + return num;
> +}
> +
> +/**
> + * __ffs - find first set bit in a long word
> + * @word: The word to search
> + *
> + * Undefined if no set bit exists, so code should check against 0 first.
> + */
> +#define __ffs(word) \
> + (__builtin_constant_p(word) ? \
> + (unsigned long)__builtin_ctzl(word) : \
> + variable__ffs(word))
> +
> +static __always_inline unsigned long variable__fls(unsigned long word)
> +{
> + int num;
> +
> + asm_volatile_goto(
> + ALTERNATIVE("j %l[legacy]", "nop", 0, RISCV_ISA_EXT_ZBB, 1)
> + : : : : legacy);
> +
> + asm volatile (
> + ".option push\n"
> + ".option arch,+zbb\n"
> + "clz %0, %1\n"
> + ".option pop\n"
> + : "=r" (word) : "r" (word) :);
> +
> + return BITS_PER_LONG - 1 - word;
> +
> +legacy:
> + num = BITS_PER_LONG - 1;
> +#if BITS_PER_LONG == 64
> + if (!(word & (~0ul << 32))) {
> + num -= 32;
> + word <<= 32;
> + }
> +#endif
> + if (!(word & (~0ul << (BITS_PER_LONG-16)))) {
> + num -= 16;
> + word <<= 16;
> + }
> + if (!(word & (~0ul << (BITS_PER_LONG-8)))) {
> + num -= 8;
> + word <<= 8;
> + }
> + if (!(word & (~0ul << (BITS_PER_LONG-4)))) {
> + num -= 4;
> + word <<= 4;
> + }
> + if (!(word & (~0ul << (BITS_PER_LONG-2)))) {
> + num -= 2;
> + word <<= 2;
> + }
> + if (!(word & (~0ul << (BITS_PER_LONG-1))))
> + num -= 1;
> + return num;
> +}
> +
> +/**
> + * __fls - find last set bit in a long word
> + * @word: the word to search
> + *
> + * Undefined if no set bit exists, so code should check against 0 first.
> + */
> +#define __fls(word) \
> + (__builtin_constant_p(word) ? \
> + (unsigned long)(BITS_PER_LONG - 1 - __builtin_clzl(word)) : \
> + variable__fls(word))
> +
> +static __always_inline int variable_ffs(int x)
> +{
> + int r;
> +
> + asm_volatile_goto(
> + ALTERNATIVE("j %l[legacy]", "nop", 0, RISCV_ISA_EXT_ZBB, 1)
> + : : : : legacy);
> +
> + asm volatile (
> + ".option push\n"
> + ".option arch,+zbb\n"
> + "bnez %1, 1f\n"
> + "li %0, 0\n"
> + "j 2f\n"
> + "1:\n"
> + CTZW "%0, %1\n"
> + "addi %0, %0, 1\n"
> + "2:\n"
> + ".option pop\n"
> + : "=r" (r) : "r" (x) :);
> +
> + return r;
> +
I generally like to move as much code out of asm as possible. You are
also able to remove one of the branches if you rearrange as follows:
if (!x)
return 0;
asm volatile (
".option push\n"
".option arch,+zbb\n"
CTZW "%0, %1\n"
".option pop\n"
: "=r" (r) : "r" (x) :);
return r + 1;
You could then also extract out the "if (!x)" at the beginning of the
legacy section at put it at the top of the function.
> +legacy:
> + r = 1;
> + if (!x)
> + return 0;
> + if (!(x & 0xffff)) {
> + x >>= 16;
> + r += 16;
> + }
> + if (!(x & 0xff)) {
> + x >>= 8;
> + r += 8;
> + }
> + if (!(x & 0xf)) {
> + x >>= 4;
> + r += 4;
> + }
> + if (!(x & 3)) {
> + x >>= 2;
> + r += 2;
> + }
> + if (!(x & 1)) {
> + x >>= 1;
> + r += 1;
> + }
> + return r;
> +}
> +
> +/**
> + * ffs - find first set bit in a word
> + * @x: the word to search
> + *
> + * This is defined the same way as the libc and compiler builtin ffs routines.
> + *
> + * ffs(value) returns 0 if value is 0 or the position of the first set bit if
> + * value is nonzero. The first (least significant) bit is at position 1.
> + */
> +#define ffs(x) (__builtin_constant_p(x) ? __builtin_ffs(x) : variable_ffs(x))
> +
> +static __always_inline int variable_fls(unsigned int x)
> +{
> + int r;
> +
> + asm_volatile_goto(
> + ALTERNATIVE("j %l[legacy]", "nop", 0, RISCV_ISA_EXT_ZBB, 1)
> + : : : : legacy);
> +
> + asm volatile (
> + ".option push\n"
> + ".option arch,+zbb\n"
> + "bnez %1, 1f\n"
> + "li %0, 0\n"
> + "j 2f\n"
> + "1:\n"
> + CLZW "%0, %1\n"
> + "neg %0, %0\n"
> + "addi %0, %0, 32\n"
> + "2:\n"
> + ".option pop\n"
> + : "=r" (r) : "r" (x) :);
> +
> + return r;
> +
Same comment as above but with appropriate changes.
> +legacy:
> + r = 32;
> + if (!x)
> + return 0;
> + if (!(x & 0xffff0000u)) {
> + x <<= 16;
> + r -= 16;
> + }
> + if (!(x & 0xff000000u)) {
> + x <<= 8;
> + r -= 8;
> + }
> + if (!(x & 0xf0000000u)) {
> + x <<= 4;
> + r -= 4;
> + }
> + if (!(x & 0xc0000000u)) {
> + x <<= 2;
> + r -= 2;
> + }
> + if (!(x & 0x80000000u)) {
> + x <<= 1;
> + r -= 1;
> + }
> + return r;
> +}
> +
> +/**
> + * fls - find last set bit in a word
> + * @x: the word to search
> + *
> + * This is defined in a similar way as ffs, but returns the position of the most
> + * significant set bit.
> + *
> + * fls(value) returns 0 if value is 0 or the position of the last set bit if
> + * value is nonzero. The last (most significant) bit is at position 32.
> + */
> +#define fls(x) \
> + (__builtin_constant_p(x) ? \
> + (int)(((x) != 0) ? \
> + (sizeof(unsigned int) * 8 - __builtin_clz(x)) : 0) : \
> + variable_fls(x))
> +
> +#endif
As a nit, it's nice when large #ifdef blocks have a comment like
/* !defined(CONFIG_RISCV_ISA_ZBB) || defined(NO_ALTERNATIVE) */
Overall great changes, just that small optimization to get rid of the
jump.
- Charlie
> +
> +#include <asm-generic/bitops/ffz.h>
> #include <asm-generic/bitops/fls64.h>
> #include <asm-generic/bitops/sched.h>
> -#include <asm-generic/bitops/ffs.h>
>
> #include <asm-generic/bitops/hweight.h>
>
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index a1157c2a7170..d68cacd4e3af 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -28,7 +28,7 @@ cflags-$(CONFIG_ARM) += -DEFI_HAVE_STRLEN -DEFI_HAVE_STRNLEN \
> -DEFI_HAVE_MEMCHR -DEFI_HAVE_STRRCHR \
> -DEFI_HAVE_STRCMP -fno-builtin -fpic \
> $(call cc-option,-mno-single-pic-base)
> -cflags-$(CONFIG_RISCV) += -fpic
> +cflags-$(CONFIG_RISCV) += -fpic -DNO_ALTERNATIVE
> cflags-$(CONFIG_LOONGARCH) += -fpie
>
> cflags-$(CONFIG_EFI_PARAMS_FROM_FDT) += -I$(srctree)/scripts/dtc/libfdt
> --
> 2.25.1
>
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
^ permalink raw reply [flat|nested] 5+ messages in thread
* RE: [PATCH v3 2/2] riscv: Optimize bitops with Zbb extension
2023-10-27 6:24 ` Charlie Jenkins
@ 2023-10-30 2:12 ` Wang, Xiao W
0 siblings, 0 replies; 5+ messages in thread
From: Wang, Xiao W @ 2023-10-30 2:12 UTC (permalink / raw)
To: Charlie Jenkins
Cc: paul.walmsley@sifive.com, palmer@dabbelt.com,
aou@eecs.berkeley.edu, ardb@kernel.org, anup@brainfault.org,
Li, Haicheng, ajones@ventanamicro.com, Liu, Yujie,
linux-riscv@lists.infradead.org, linux-efi@vger.kernel.org,
linux-kernel@vger.kernel.org
> -----Original Message-----
> From: Charlie Jenkins <charlie@rivosinc.com>
> Sent: Friday, October 27, 2023 2:25 PM
> To: Wang, Xiao W <xiao.w.wang@intel.com>
> Cc: paul.walmsley@sifive.com; palmer@dabbelt.com;
> aou@eecs.berkeley.edu; ardb@kernel.org; anup@brainfault.org; Li, Haicheng
> <haicheng.li@intel.com>; ajones@ventanamicro.com; Liu, Yujie
> <yujie.liu@intel.com>; linux-riscv@lists.infradead.org; linux-
> efi@vger.kernel.org; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH v3 2/2] riscv: Optimize bitops with Zbb extension
>
> On Tue, Sep 26, 2023 at 05:46:55PM +0800, Xiao Wang wrote:
> > This patch leverages the alternative mechanism to dynamically optimize
> > bitops (including __ffs, __fls, ffs, fls) with Zbb instructions. When
> > Zbb ext is not supported by the runtime CPU, legacy implementation is
> > used. If Zbb is supported, then the optimized variants will be selected
> > via alternative patching.
> >
> > The legacy bitops support is taken from the generic C implementation as
> > fallback.
> >
> > If the parameter is a build-time constant, we leverage compiler builtin to
> > calculate the result directly, this approach is inspired by x86 bitops
> > implementation.
> >
> > EFI stub runs before the kernel, so alternative mechanism should not be
> > used there, this patch introduces a macro NO_ALTERNATIVE for this
> purpose.
> >
> > Signed-off-by: Xiao Wang <xiao.w.wang@intel.com>
> > ---
> > arch/riscv/include/asm/bitops.h | 266 +++++++++++++++++++++++++-
> > drivers/firmware/efi/libstub/Makefile | 2 +-
> > 2 files changed, 264 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/bitops.h
> b/arch/riscv/include/asm/bitops.h
> > index 3540b690944b..c97e774cb647 100644
> > --- a/arch/riscv/include/asm/bitops.h
> > +++ b/arch/riscv/include/asm/bitops.h
> > @@ -15,13 +15,273 @@
> > #include <asm/barrier.h>
> > #include <asm/bitsperlong.h>
> >
> > +#if !defined(CONFIG_RISCV_ISA_ZBB) || defined(NO_ALTERNATIVE)
> > #include <asm-generic/bitops/__ffs.h>
> > -#include <asm-generic/bitops/ffz.h>
> > -#include <asm-generic/bitops/fls.h>
> > #include <asm-generic/bitops/__fls.h>
> > +#include <asm-generic/bitops/ffs.h>
> > +#include <asm-generic/bitops/fls.h>
> > +
> > +#else
> > +#include <asm/alternative-macros.h>
> > +#include <asm/hwcap.h>
> > +
> > +#if (BITS_PER_LONG == 64)
> > +#define CTZW "ctzw "
> > +#define CLZW "clzw "
> > +#elif (BITS_PER_LONG == 32)
> > +#define CTZW "ctz "
> > +#define CLZW "clz "
> > +#else
> > +#error "Unexpected BITS_PER_LONG"
> > +#endif
> > +
> > +static __always_inline unsigned long variable__ffs(unsigned long word)
> > +{
> > + int num;
> > +
> > + asm_volatile_goto(
> > + ALTERNATIVE("j %l[legacy]", "nop", 0, RISCV_ISA_EXT_ZBB, 1)
> > + : : : : legacy);
> > +
> > + asm volatile (
> > + ".option push\n"
> > + ".option arch,+zbb\n"
> > + "ctz %0, %1\n"
> > + ".option pop\n"
> > + : "=r" (word) : "r" (word) :);
> > +
> > + return word;
>
> That's so clean!
>
> > +
> > +legacy:
> > + num = 0;
> > +#if BITS_PER_LONG == 64
> > + if ((word & 0xffffffff) == 0) {
> > + num += 32;
> > + word >>= 32;
> > + }
> > +#endif
> > + if ((word & 0xffff) == 0) {
> > + num += 16;
> > + word >>= 16;
> > + }
> > + if ((word & 0xff) == 0) {
> > + num += 8;
> > + word >>= 8;
> > + }
> > + if ((word & 0xf) == 0) {
> > + num += 4;
> > + word >>= 4;
> > + }
> > + if ((word & 0x3) == 0) {
> > + num += 2;
> > + word >>= 2;
> > + }
> > + if ((word & 0x1) == 0)
> > + num += 1;
> > + return num;
> > +}
> > +
> > +/**
> > + * __ffs - find first set bit in a long word
> > + * @word: The word to search
> > + *
> > + * Undefined if no set bit exists, so code should check against 0 first.
> > + */
> > +#define __ffs(word) \
> > + (__builtin_constant_p(word) ? \
> > + (unsigned long)__builtin_ctzl(word) : \
> > + variable__ffs(word))
> > +
> > +static __always_inline unsigned long variable__fls(unsigned long word)
> > +{
> > + int num;
> > +
> > + asm_volatile_goto(
> > + ALTERNATIVE("j %l[legacy]", "nop", 0, RISCV_ISA_EXT_ZBB, 1)
> > + : : : : legacy);
> > +
> > + asm volatile (
> > + ".option push\n"
> > + ".option arch,+zbb\n"
> > + "clz %0, %1\n"
> > + ".option pop\n"
> > + : "=r" (word) : "r" (word) :);
> > +
> > + return BITS_PER_LONG - 1 - word;
> > +
> > +legacy:
> > + num = BITS_PER_LONG - 1;
> > +#if BITS_PER_LONG == 64
> > + if (!(word & (~0ul << 32))) {
> > + num -= 32;
> > + word <<= 32;
> > + }
> > +#endif
> > + if (!(word & (~0ul << (BITS_PER_LONG-16)))) {
> > + num -= 16;
> > + word <<= 16;
> > + }
> > + if (!(word & (~0ul << (BITS_PER_LONG-8)))) {
> > + num -= 8;
> > + word <<= 8;
> > + }
> > + if (!(word & (~0ul << (BITS_PER_LONG-4)))) {
> > + num -= 4;
> > + word <<= 4;
> > + }
> > + if (!(word & (~0ul << (BITS_PER_LONG-2)))) {
> > + num -= 2;
> > + word <<= 2;
> > + }
> > + if (!(word & (~0ul << (BITS_PER_LONG-1))))
> > + num -= 1;
> > + return num;
> > +}
> > +
> > +/**
> > + * __fls - find last set bit in a long word
> > + * @word: the word to search
> > + *
> > + * Undefined if no set bit exists, so code should check against 0 first.
> > + */
> > +#define __fls(word) \
> > + (__builtin_constant_p(word) ? \
> > + (unsigned long)(BITS_PER_LONG - 1 - __builtin_clzl(word)) : \
> > + variable__fls(word))
> > +
> > +static __always_inline int variable_ffs(int x)
> > +{
> > + int r;
> > +
> > + asm_volatile_goto(
> > + ALTERNATIVE("j %l[legacy]", "nop", 0, RISCV_ISA_EXT_ZBB, 1)
> > + : : : : legacy);
> > +
> > + asm volatile (
> > + ".option push\n"
> > + ".option arch,+zbb\n"
> > + "bnez %1, 1f\n"
> > + "li %0, 0\n"
> > + "j 2f\n"
> > + "1:\n"
> > + CTZW "%0, %1\n"
> > + "addi %0, %0, 1\n"
> > + "2:\n"
> > + ".option pop\n"
> > + : "=r" (r) : "r" (x) :);
> > +
> > + return r;
> > +
>
> I generally like to move as much code out of asm as possible. You are
> also able to remove one of the branches if you rearrange as follows:
>
> if (!x)
> return 0;
>
> asm volatile (
> ".option push\n"
> ".option arch,+zbb\n"
> CTZW "%0, %1\n"
> ".option pop\n"
> : "=r" (r) : "r" (x) :);
>
> return r + 1;
>
> You could then also extract out the "if (!x)" at the beginning of the
> legacy section at put it at the top of the function.
>
Agree, less asm code will be more reader friendly. And your sample code looks
nice, thanks for the suggestion. Will do the adjustment in next version.
> > +legacy:
> > + r = 1;
> > + if (!x)
> > + return 0;
> > + if (!(x & 0xffff)) {
> > + x >>= 16;
> > + r += 16;
> > + }
> > + if (!(x & 0xff)) {
> > + x >>= 8;
> > + r += 8;
> > + }
> > + if (!(x & 0xf)) {
> > + x >>= 4;
> > + r += 4;
> > + }
> > + if (!(x & 3)) {
> > + x >>= 2;
> > + r += 2;
> > + }
> > + if (!(x & 1)) {
> > + x >>= 1;
> > + r += 1;
> > + }
> > + return r;
> > +}
> > +
> > +/**
> > + * ffs - find first set bit in a word
> > + * @x: the word to search
> > + *
> > + * This is defined the same way as the libc and compiler builtin ffs routines.
> > + *
> > + * ffs(value) returns 0 if value is 0 or the position of the first set bit if
> > + * value is nonzero. The first (least significant) bit is at position 1.
> > + */
> > +#define ffs(x) (__builtin_constant_p(x) ? __builtin_ffs(x) : variable_ffs(x))
> > +
> > +static __always_inline int variable_fls(unsigned int x)
> > +{
> > + int r;
> > +
> > + asm_volatile_goto(
> > + ALTERNATIVE("j %l[legacy]", "nop", 0, RISCV_ISA_EXT_ZBB, 1)
> > + : : : : legacy);
> > +
> > + asm volatile (
> > + ".option push\n"
> > + ".option arch,+zbb\n"
> > + "bnez %1, 1f\n"
> > + "li %0, 0\n"
> > + "j 2f\n"
> > + "1:\n"
> > + CLZW "%0, %1\n"
> > + "neg %0, %0\n"
> > + "addi %0, %0, 32\n"
> > + "2:\n"
> > + ".option pop\n"
> > + : "=r" (r) : "r" (x) :);
> > +
> > + return r;
> > +
>
> Same comment as above but with appropriate changes.
Will refine it in next version.
>
> > +legacy:
> > + r = 32;
> > + if (!x)
> > + return 0;
> > + if (!(x & 0xffff0000u)) {
> > + x <<= 16;
> > + r -= 16;
> > + }
> > + if (!(x & 0xff000000u)) {
> > + x <<= 8;
> > + r -= 8;
> > + }
> > + if (!(x & 0xf0000000u)) {
> > + x <<= 4;
> > + r -= 4;
> > + }
> > + if (!(x & 0xc0000000u)) {
> > + x <<= 2;
> > + r -= 2;
> > + }
> > + if (!(x & 0x80000000u)) {
> > + x <<= 1;
> > + r -= 1;
> > + }
> > + return r;
> > +}
> > +
> > +/**
> > + * fls - find last set bit in a word
> > + * @x: the word to search
> > + *
> > + * This is defined in a similar way as ffs, but returns the position of the most
> > + * significant set bit.
> > + *
> > + * fls(value) returns 0 if value is 0 or the position of the last set bit if
> > + * value is nonzero. The last (most significant) bit is at position 32.
> > + */
> > +#define fls(x)
> \
> > + (__builtin_constant_p(x) ? \
> > + (int)(((x) != 0) ? \
> > + (sizeof(unsigned int) * 8 - __builtin_clz(x)) : 0) : \
> > + variable_fls(x))
> > +
> > +#endif
>
> As a nit, it's nice when large #ifdef blocks have a comment like
>
> /* !defined(CONFIG_RISCV_ISA_ZBB) || defined(NO_ALTERNATIVE) */
>
Yes, I will add it in next version. Thanks for the comments.
BRs,
Xiao
> Overall great changes, just that small optimization to get rid of the
> jump.
>
> - Charlie
>
> > +
> > +#include <asm-generic/bitops/ffz.h>
> > #include <asm-generic/bitops/fls64.h>
> > #include <asm-generic/bitops/sched.h>
> > -#include <asm-generic/bitops/ffs.h>
> >
> > #include <asm-generic/bitops/hweight.h>
> >
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^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2023-10-30 2:12 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2023-09-26 9:46 [PATCH v3 0/2] riscv: Optimize bitops with Zbb extension Xiao Wang
2023-09-26 9:46 ` [PATCH v3 1/2] riscv: Rearrange hwcap.h and cpufeature.h Xiao Wang
2023-09-26 9:46 ` [PATCH v3 2/2] riscv: Optimize bitops with Zbb extension Xiao Wang
2023-10-27 6:24 ` Charlie Jenkins
2023-10-30 2:12 ` Wang, Xiao W
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