* [PATCH v4 1/2] riscv: use vDSO common flow to reduce the latency of the time-related functions
2020-06-09 14:14 [PATCH v4 0/2] riscv: introduce vDSO common flow Vincent Chen
@ 2020-06-09 14:14 ` Vincent Chen
2020-06-09 14:14 ` [PATCH v4 2/2] riscv: set the permission of vdso_data to read-only Vincent Chen
2020-06-11 2:50 ` [PATCH v4 0/2] riscv: introduce vDSO common flow Palmer Dabbelt
2 siblings, 0 replies; 4+ messages in thread
From: Vincent Chen @ 2020-06-09 14:14 UTC (permalink / raw)
To: palmer, paul.walmsley; +Cc: Vincent Chen, linux-riscv, Palmer Dabbelt
Even if RISC-V has supported the vDSO feature, the latency of the functions
for obtaining the system time is still expensive. It is because these
functions still trigger a corresponding system call in the process, which
slows down the response time. If we want to remove the system call to
reduce the latency, the kernel should have the ability to output the system
clock information to userspace. This patch introduces the vDSO common flow
to enable the kernel to achieve the above feature and uses "rdtime"
instruction to obtain the current time in the user space. Under this
condition, the latency cost by the ecall from U-mode to S-mode can be
eliminated. After applying this patch, the latency of gettimeofday()
measured on the HiFive unleashed board can be reduced by %61.
Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
---
arch/riscv/Kconfig | 4 ++
arch/riscv/include/asm/clocksource.h | 7 ++
arch/riscv/include/asm/processor.h | 12 +---
arch/riscv/include/asm/vdso.h | 2 +
arch/riscv/include/asm/vdso/clocksource.h | 8 +++
arch/riscv/include/asm/vdso/gettimeofday.h | 79 ++++++++++++++++++++++
arch/riscv/include/asm/vdso/processor.h | 19 ++++++
arch/riscv/include/asm/vdso/vsyscall.h | 27 ++++++++
arch/riscv/kernel/time.c | 9 +++
arch/riscv/kernel/vdso.c | 8 ++-
arch/riscv/kernel/vdso/Makefile | 12 +++-
arch/riscv/kernel/vdso/clock_getres.S | 18 -----
arch/riscv/kernel/vdso/clock_gettime.S | 18 -----
arch/riscv/kernel/vdso/gettimeofday.S | 18 -----
arch/riscv/kernel/vdso/vdso.lds.S | 2 +
arch/riscv/kernel/vdso/vgettimeofday.c | 25 +++++++
16 files changed, 199 insertions(+), 69 deletions(-)
create mode 100644 arch/riscv/include/asm/clocksource.h
create mode 100644 arch/riscv/include/asm/vdso/clocksource.h
create mode 100644 arch/riscv/include/asm/vdso/gettimeofday.h
create mode 100644 arch/riscv/include/asm/vdso/processor.h
create mode 100644 arch/riscv/include/asm/vdso/vsyscall.h
delete mode 100644 arch/riscv/kernel/vdso/clock_getres.S
delete mode 100644 arch/riscv/kernel/vdso/clock_gettime.S
delete mode 100644 arch/riscv/kernel/vdso/gettimeofday.S
create mode 100644 arch/riscv/kernel/vdso/vgettimeofday.c
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 8244b8f7e7c3..d0419ab1fed0 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -12,6 +12,7 @@ config 32BIT
config RISCV
def_bool y
+ select ARCH_CLOCKSOURCE_INIT
select ARCH_HAS_BINFMT_FLAT
select ARCH_HAS_DEBUG_VIRTUAL if MMU
select ARCH_HAS_DEBUG_WX
@@ -31,6 +32,7 @@ config RISCV
select GENERIC_ARCH_TOPOLOGY if SMP
select GENERIC_ATOMIC64 if !64BIT
select GENERIC_CLOCKEVENTS
+ select GENERIC_GETTIMEOFDAY if HAVE_GENERIC_VDSO
select GENERIC_IOREMAP
select GENERIC_IRQ_MULTI_HANDLER
select GENERIC_IRQ_SHOW
@@ -40,6 +42,7 @@ config RISCV
select GENERIC_SMP_IDLE_THREAD
select GENERIC_STRNCPY_FROM_USER if MMU
select GENERIC_STRNLEN_USER if MMU
+ select GENERIC_TIME_VSYSCALL if MMU && 64BIT
select HAVE_ARCH_AUDITSYSCALL
select HAVE_ARCH_KASAN if MMU && 64BIT
select HAVE_ARCH_KGDB
@@ -52,6 +55,7 @@ config RISCV
select HAVE_DMA_CONTIGUOUS if MMU
select HAVE_EBPF_JIT if MMU
select HAVE_FUTEX_CMPXCHG if FUTEX
+ select HAVE_GENERIC_VDSO if MMU && 64BIT
select HAVE_PCI
select HAVE_PERF_EVENTS
select HAVE_PERF_REGS
diff --git a/arch/riscv/include/asm/clocksource.h b/arch/riscv/include/asm/clocksource.h
new file mode 100644
index 000000000000..482185566b0c
--- /dev/null
+++ b/arch/riscv/include/asm/clocksource.h
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_CLOCKSOURCE_H
+#define _ASM_CLOCKSOURCE_H
+
+#include <asm/vdso/clocksource.h>
+
+#endif
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 3ddb798264f1..d6117b316e2b 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -8,6 +8,8 @@
#include <linux/const.h>
+#include <vdso/processor.h>
+
#include <asm/ptrace.h>
/*
@@ -58,16 +60,6 @@ static inline void release_thread(struct task_struct *dead_task)
extern unsigned long get_wchan(struct task_struct *p);
-static inline void cpu_relax(void)
-{
-#ifdef __riscv_muldiv
- int dummy;
- /* In lieu of a halt instruction, induce a long-latency stall. */
- __asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
-#endif
- barrier();
-}
-
static inline void wait_for_interrupt(void)
{
__asm__ __volatile__ ("wfi");
diff --git a/arch/riscv/include/asm/vdso.h b/arch/riscv/include/asm/vdso.h
index 7a7fce63c474..8454f746bbfd 100644
--- a/arch/riscv/include/asm/vdso.h
+++ b/arch/riscv/include/asm/vdso.h
@@ -10,8 +10,10 @@
#include <linux/types.h>
+#ifndef GENERIC_TIME_VSYSCALL
struct vdso_data {
};
+#endif
/*
* The VDSO symbols are mapped into Linux so we can just use regular symbol
diff --git a/arch/riscv/include/asm/vdso/clocksource.h b/arch/riscv/include/asm/vdso/clocksource.h
new file mode 100644
index 000000000000..df6ea65c1dec
--- /dev/null
+++ b/arch/riscv/include/asm/vdso/clocksource.h
@@ -0,0 +1,8 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_VDSOCLOCKSOURCE_H
+#define __ASM_VDSOCLOCKSOURCE_H
+
+#define VDSO_ARCH_CLOCKMODES \
+ VDSO_CLOCKMODE_ARCHTIMER
+
+#endif
diff --git a/arch/riscv/include/asm/vdso/gettimeofday.h b/arch/riscv/include/asm/vdso/gettimeofday.h
new file mode 100644
index 000000000000..c8e818688ec1
--- /dev/null
+++ b/arch/riscv/include/asm/vdso/gettimeofday.h
@@ -0,0 +1,79 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_VDSO_GETTIMEOFDAY_H
+#define __ASM_VDSO_GETTIMEOFDAY_H
+
+#ifndef __ASSEMBLY__
+
+#include <asm/unistd.h>
+#include <asm/csr.h>
+#include <uapi/linux/time.h>
+
+#define VDSO_HAS_CLOCK_GETRES 1
+
+static __always_inline
+int gettimeofday_fallback(struct __kernel_old_timeval *_tv,
+ struct timezone *_tz)
+{
+ register struct __kernel_old_timeval *tv asm("a0") = _tv;
+ register struct timezone *tz asm("a1") = _tz;
+ register long ret asm("a0");
+ register long nr asm("a7") = __NR_gettimeofday;
+
+ asm volatile ("ecall\n"
+ : "=r" (ret)
+ : "r"(tv), "r"(tz), "r"(nr)
+ : "memory");
+
+ return ret;
+}
+
+static __always_inline
+long clock_gettime_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
+{
+ register clockid_t clkid asm("a0") = _clkid;
+ register struct __kernel_timespec *ts asm("a1") = _ts;
+ register long ret asm("a0");
+ register long nr asm("a7") = __NR_clock_gettime;
+
+ asm volatile ("ecall\n"
+ : "=r" (ret)
+ : "r"(clkid), "r"(ts), "r"(nr)
+ : "memory");
+
+ return ret;
+}
+
+static __always_inline
+int clock_getres_fallback(clockid_t _clkid, struct __kernel_timespec *_ts)
+{
+ register clockid_t clkid asm("a0") = _clkid;
+ register struct __kernel_timespec *ts asm("a1") = _ts;
+ register long ret asm("a0");
+ register long nr asm("a7") = __NR_clock_getres;
+
+ asm volatile ("ecall\n"
+ : "=r" (ret)
+ : "r"(clkid), "r"(ts), "r"(nr)
+ : "memory");
+
+ return ret;
+}
+
+static __always_inline u64 __arch_get_hw_counter(s32 clock_mode)
+{
+ /*
+ * The purpose of csr_read(CSR_TIME) is to trap the system into
+ * M-mode to obtain the value of CSR_TIME. Hence, unlike other
+ * architecture, no fence instructions surround the csr_read()
+ */
+ return csr_read(CSR_TIME);
+}
+
+static __always_inline const struct vdso_data *__arch_get_vdso_data(void)
+{
+ return _vdso_data;
+}
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* __ASM_VDSO_GETTIMEOFDAY_H */
diff --git a/arch/riscv/include/asm/vdso/processor.h b/arch/riscv/include/asm/vdso/processor.h
new file mode 100644
index 000000000000..82a5693b1861
--- /dev/null
+++ b/arch/riscv/include/asm/vdso/processor.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef __ASM_VDSO_PROCESSOR_H
+#define __ASM_VDSO_PROCESSOR_H
+
+#ifndef __ASSEMBLY__
+
+static inline void cpu_relax(void)
+{
+#ifdef __riscv_muldiv
+ int dummy;
+ /* In lieu of a halt instruction, induce a long-latency stall. */
+ __asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
+#endif
+ barrier();
+}
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* __ASM_VDSO_PROCESSOR_H */
diff --git a/arch/riscv/include/asm/vdso/vsyscall.h b/arch/riscv/include/asm/vdso/vsyscall.h
new file mode 100644
index 000000000000..82fd5d83bd60
--- /dev/null
+++ b/arch/riscv/include/asm/vdso/vsyscall.h
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_VDSO_VSYSCALL_H
+#define __ASM_VDSO_VSYSCALL_H
+
+#ifndef __ASSEMBLY__
+
+#include <linux/timekeeper_internal.h>
+#include <vdso/datapage.h>
+
+extern struct vdso_data *vdso_data;
+
+/*
+ * Update the vDSO data page to keep in sync with kernel timekeeping.
+ */
+static __always_inline struct vdso_data *__riscv_get_k_vdso_data(void)
+{
+ return vdso_data;
+}
+
+#define __arch_get_k_vdso_data __riscv_get_k_vdso_data
+
+/* The asm-generic header needs to be included after the definitions above */
+#include <asm-generic/vdso/vsyscall.h>
+
+#endif /* !__ASSEMBLY__ */
+
+#endif /* __ASM_VDSO_VSYSCALL_H */
diff --git a/arch/riscv/kernel/time.c b/arch/riscv/kernel/time.c
index 6a53c02e9c73..4d3a1048ad8b 100644
--- a/arch/riscv/kernel/time.c
+++ b/arch/riscv/kernel/time.c
@@ -26,3 +26,12 @@ void __init time_init(void)
lpj_fine = riscv_timebase / HZ;
timer_probe();
}
+
+void clocksource_arch_init(struct clocksource *cs)
+{
+#ifdef CONFIG_GENERIC_GETTIMEOFDAY
+ cs->vdso_clock_mode = VDSO_CLOCKMODE_ARCHTIMER;
+#else
+ cs->vdso_clock_mode = VDSO_CLOCKMODE_NONE;
+#endif
+}
diff --git a/arch/riscv/kernel/vdso.c b/arch/riscv/kernel/vdso.c
index 484d95a70907..70b6461a6387 100644
--- a/arch/riscv/kernel/vdso.c
+++ b/arch/riscv/kernel/vdso.c
@@ -11,8 +11,12 @@
#include <linux/slab.h>
#include <linux/binfmts.h>
#include <linux/err.h>
-
+#include <asm/page.h>
+#ifdef GENERIC_TIME_VSYSCALL
+#include <vdso/datapage.h>
+#else
#include <asm/vdso.h>
+#endif
extern char vdso_start[], vdso_end[];
@@ -26,7 +30,7 @@ static union {
struct vdso_data data;
u8 page[PAGE_SIZE];
} vdso_data_store __page_aligned_data;
-static struct vdso_data *vdso_data = &vdso_data_store.data;
+struct vdso_data *vdso_data = &vdso_data_store.data;
static int __init vdso_init(void)
{
diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
index 4c8b2a4a6a70..38ba55b0eb9d 100644
--- a/arch/riscv/kernel/vdso/Makefile
+++ b/arch/riscv/kernel/vdso/Makefile
@@ -1,12 +1,14 @@
# SPDX-License-Identifier: GPL-2.0-only
# Copied from arch/tile/kernel/vdso/Makefile
+# Absolute relocation type $(ARCH_REL_TYPE_ABS) needs to be defined before
+# the inclusion of generic Makefile.
+ARCH_REL_TYPE_ABS := R_RISCV_32|R_RISCV_64|R_RISCV_JUMP_SLOT
+include $(srctree)/lib/vdso/Makefile
# Symbols present in the vdso
vdso-syms = rt_sigreturn
ifdef CONFIG_64BIT
-vdso-syms += gettimeofday
-vdso-syms += clock_gettime
-vdso-syms += clock_getres
+vdso-syms += vgettimeofday
endif
vdso-syms += getcpu
vdso-syms += flush_icache
@@ -14,6 +16,10 @@ vdso-syms += flush_icache
# Files to link into the vdso
obj-vdso = $(patsubst %, %.o, $(vdso-syms)) note.o
+ifneq ($(c-gettimeofday-y),)
+ CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
+endif
+
# Build rules
targets := $(obj-vdso) vdso.so vdso.so.dbg vdso.lds vdso-dummy.o
obj-vdso := $(addprefix $(obj)/, $(obj-vdso))
diff --git a/arch/riscv/kernel/vdso/clock_getres.S b/arch/riscv/kernel/vdso/clock_getres.S
deleted file mode 100644
index 91378a52eb22..000000000000
--- a/arch/riscv/kernel/vdso/clock_getres.S
+++ /dev/null
@@ -1,18 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-/*
- * Copyright (C) 2017 SiFive
- */
-
-#include <linux/linkage.h>
-#include <asm/unistd.h>
-
- .text
-/* int __vdso_clock_getres(clockid_t clock_id, struct timespec *res); */
-ENTRY(__vdso_clock_getres)
- .cfi_startproc
- /* For now, just do the syscall. */
- li a7, __NR_clock_getres
- ecall
- ret
- .cfi_endproc
-ENDPROC(__vdso_clock_getres)
diff --git a/arch/riscv/kernel/vdso/clock_gettime.S b/arch/riscv/kernel/vdso/clock_gettime.S
deleted file mode 100644
index 5371fd9bc01f..000000000000
--- a/arch/riscv/kernel/vdso/clock_gettime.S
+++ /dev/null
@@ -1,18 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-/*
- * Copyright (C) 2017 SiFive
- */
-
-#include <linux/linkage.h>
-#include <asm/unistd.h>
-
- .text
-/* int __vdso_clock_gettime(clockid_t clock_id, struct timespec *tp); */
-ENTRY(__vdso_clock_gettime)
- .cfi_startproc
- /* For now, just do the syscall. */
- li a7, __NR_clock_gettime
- ecall
- ret
- .cfi_endproc
-ENDPROC(__vdso_clock_gettime)
diff --git a/arch/riscv/kernel/vdso/gettimeofday.S b/arch/riscv/kernel/vdso/gettimeofday.S
deleted file mode 100644
index e6fb8af88632..000000000000
--- a/arch/riscv/kernel/vdso/gettimeofday.S
+++ /dev/null
@@ -1,18 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-/*
- * Copyright (C) 2017 SiFive
- */
-
-#include <linux/linkage.h>
-#include <asm/unistd.h>
-
- .text
-/* int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz); */
-ENTRY(__vdso_gettimeofday)
- .cfi_startproc
- /* For now, just do the syscall. */
- li a7, __NR_gettimeofday
- ecall
- ret
- .cfi_endproc
-ENDPROC(__vdso_gettimeofday)
diff --git a/arch/riscv/kernel/vdso/vdso.lds.S b/arch/riscv/kernel/vdso/vdso.lds.S
index f66a091cb890..e6f558bca71b 100644
--- a/arch/riscv/kernel/vdso/vdso.lds.S
+++ b/arch/riscv/kernel/vdso/vdso.lds.S
@@ -2,11 +2,13 @@
/*
* Copyright (C) 2012 Regents of the University of California
*/
+#include <asm/page.h>
OUTPUT_ARCH(riscv)
SECTIONS
{
+ PROVIDE(_vdso_data = . + PAGE_SIZE);
. = SIZEOF_HEADERS;
.hash : { *(.hash) } :text
diff --git a/arch/riscv/kernel/vdso/vgettimeofday.c b/arch/riscv/kernel/vdso/vgettimeofday.c
new file mode 100644
index 000000000000..d264943e2e47
--- /dev/null
+++ b/arch/riscv/kernel/vdso/vgettimeofday.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copied from arch/arm64/kernel/vdso/vgettimeofday.c
+ *
+ * Copyright (C) 2018 ARM Ltd.
+ * Copyright (C) 2020 SiFive
+ */
+
+#include <linux/time.h>
+#include <linux/types.h>
+
+int __vdso_clock_gettime(clockid_t clock, struct __kernel_timespec *ts)
+{
+ return __cvdso_clock_gettime(clock, ts);
+}
+
+int __vdso_gettimeofday(struct __kernel_old_timeval *tv, struct timezone *tz)
+{
+ return __cvdso_gettimeofday(tv, tz);
+}
+
+int __vdso_clock_getres(clockid_t clock_id, struct __kernel_timespec *res)
+{
+ return __cvdso_clock_getres(clock_id, res);
+}
--
2.27.0
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH v4 2/2] riscv: set the permission of vdso_data to read-only
2020-06-09 14:14 [PATCH v4 0/2] riscv: introduce vDSO common flow Vincent Chen
2020-06-09 14:14 ` [PATCH v4 1/2] riscv: use vDSO common flow to reduce the latency of the time-related functions Vincent Chen
@ 2020-06-09 14:14 ` Vincent Chen
2020-06-11 2:50 ` [PATCH v4 0/2] riscv: introduce vDSO common flow Palmer Dabbelt
2 siblings, 0 replies; 4+ messages in thread
From: Vincent Chen @ 2020-06-09 14:14 UTC (permalink / raw)
To: palmer, paul.walmsley; +Cc: Vincent Chen, linux-riscv, Palmer Dabbelt
The original vdso_data page is empty, so the permission of the vdso_data
page can be the same with the vdso text page. After introducing the vDSO
common flow, the vdso_data is not empty and the permission should be
changed to read-only.
Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
---
arch/riscv/kernel/vdso.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/kernel/vdso.c b/arch/riscv/kernel/vdso.c
index 70b6461a6387..94450332aa4f 100644
--- a/arch/riscv/kernel/vdso.c
+++ b/arch/riscv/kernel/vdso.c
@@ -79,13 +79,22 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
*/
mm->context.vdso = (void *)vdso_base;
- ret = install_special_mapping(mm, vdso_base, vdso_len,
+ ret =
+ install_special_mapping(mm, vdso_base, vdso_pages << PAGE_SHIFT,
(VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC),
vdso_pagelist);
- if (unlikely(ret))
+ if (unlikely(ret)) {
mm->context.vdso = NULL;
+ goto end;
+ }
+ vdso_base += (vdso_pages << PAGE_SHIFT);
+ ret = install_special_mapping(mm, vdso_base, PAGE_SIZE,
+ (VM_READ | VM_MAYREAD), &vdso_pagelist[vdso_pages]);
+
+ if (unlikely(ret))
+ mm->context.vdso = NULL;
end:
up_write(&mm->mmap_sem);
return ret;
@@ -95,5 +104,8 @@ const char *arch_vma_name(struct vm_area_struct *vma)
{
if (vma->vm_mm && (vma->vm_start == (long)vma->vm_mm->context.vdso))
return "[vdso]";
+ if (vma->vm_mm && (vma->vm_start ==
+ (long)vma->vm_mm->context.vdso + PAGE_SIZE))
+ return "[vdso_data]";
return NULL;
}
--
2.27.0
^ permalink raw reply related [flat|nested] 4+ messages in thread