@@ -164,24 +164,7 @@ static inline void arch_timer_set_cntkctl(u32 cntkctl)
isb();
}
-/*
- * Ensure that reads of the counter are treated the same as memory reads
- * for the purposes of ordering by subsequent memory barriers.
- *
- * This insanity brought to you by speculative system register reads,
- * out-of-order memory accesses, sequence locks and Thomas Gleixner.
- *
- * http://lists.infradead.org/pipermail/linux-arm-kernel/2019-February/631195.html
- */
-#define arch_counter_enforce_ordering(val) do { \
- u64 tmp, _val = (val); \
- \
- asm volatile( \
- " eor %0, %1, %1\n" \
- " add %0, sp, %0\n" \
- " ldr xzr, [%0]" \
- : "=r" (tmp) : "r" (_val)); \
-} while (0)
+#include <asm/common/arch_timer.h>
static __always_inline u64 __arch_counter_get_cntpct_stable(void)
{
@@ -189,7 +172,7 @@ static __always_inline u64 __arch_counter_get_cntpct_stable(void)
isb();
cnt = arch_timer_reg_read_stable(cntpct_el0);
- arch_counter_enforce_ordering(cnt);
+ cnt = arch_counter_enforce_ordering(cnt);
return cnt;
}
@@ -199,7 +182,7 @@ static __always_inline u64 __arch_counter_get_cntpct(void)
isb();
cnt = read_sysreg(cntpct_el0);
- arch_counter_enforce_ordering(cnt);
+ cnt = arch_counter_enforce_ordering(cnt);
return cnt;
}
@@ -209,7 +192,7 @@ static __always_inline u64 __arch_counter_get_cntvct_stable(void)
isb();
cnt = arch_timer_reg_read_stable(cntvct_el0);
- arch_counter_enforce_ordering(cnt);
+ cnt = arch_counter_enforce_ordering(cnt);
return cnt;
}
@@ -219,12 +202,10 @@ static __always_inline u64 __arch_counter_get_cntvct(void)
isb();
cnt = read_sysreg(cntvct_el0);
- arch_counter_enforce_ordering(cnt);
+ cnt = arch_counter_enforce_ordering(cnt);
return cnt;
}
-#undef arch_counter_enforce_ordering
-
static inline int arch_timer_arch_init(void)
{
return 0;
new file mode 100644
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 ARM Ltd.
+ */
+#ifndef __ASM_COMMON_ARCH_TIMER_H
+#define __ASM_COMMON_ARCH_TIMER_H
+
+#include <uapi/linux/types.h>
+
+/*
+ * Ensure that reads of the counter are treated the same as memory reads
+ * for the purposes of ordering by subsequent memory barriers.
+ *
+ * This insanity brought to you by speculative system register reads,
+ * out-of-order memory accesses, sequence locks and Thomas Gleixner.
+ *
+ * http://lists.infradead.org/pipermail/linux-arm-kernel/2019-February/631195.html
+ *
+ */
+static u64 arch_counter_enforce_ordering(u64 val)
+{
+ u64 tmp, _val = (val);
+
+ asm volatile(
+ " eor %0, %1, %1\n"
+ " add %0, sp, %0\n"
+ " ldr xzr, [%0]"
+ : "=r" (tmp) : "r" (_val));
+
+ return _val;
+}
+
+#endif /* __ASM_COMMON_ARCH_TIMER_H */
@@ -8,6 +8,7 @@
#ifndef __ASSEMBLY__
#include <asm/unistd.h>
+#include <asm/common/arch_timer.h>
#define __VDSO_USE_SYSCALL ULLONG_MAX
@@ -83,10 +84,10 @@ static __always_inline u64 __arch_get_hw_counter(s32 clock_mode)
isb();
asm volatile("mrs %0, cntvct_el0" : "=r" (res) :: "memory");
/*
- * This isb() is required to prevent that the seq lock is
- * speculated.#
+ * arch_counter_enforce_ordering() is required to prevent that
+ * the seq lock is speculated.
*/
- isb();
+ res = arch_counter_enforce_ordering(res);
return res;
}
The vDSO library should only include the necessary headers required for a userspace library (UAPI and a minimal set of kernel headers). To make this possible it is necessary to isolate from the kernel headers the common parts that are strictly necessary to build the library. Introduce asm/common/arch_timer.h to contain all the arm64 specific code. This allows to replace the second isb() in __arch_get_hw_counter() with a fake dependent stack read of the counter which improves the vdso library peformances of ~4.5%. Below the results of vdsotest [1] ran for 100 iterations. Before the patch: ================= clock-gettime-monotonic: syscall: 771 nsec/call clock-gettime-monotonic: libc: 130 nsec/call clock-gettime-monotonic: vdso: 111 nsec/call ... clock-gettime-realtime: syscall: 762 nsec/call clock-gettime-realtime: libc: 130 nsec/call clock-gettime-realtime: vdso: 111 nsec/call After the patch: ================ clock-gettime-monotonic: syscall: 792 nsec/call clock-gettime-monotonic: libc: 124 nsec/call clock-gettime-monotonic: vdso: 106 nsec/call ... clock-gettime-realtime: syscall: 776 nsec/call clock-gettime-realtime: libc: 124 nsec/call clock-gettime-realtime: vdso: 106 nsec/call [1] https://github.com/nathanlynch/vdsotest Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will@kernel.org> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com> --- arch/arm64/include/asm/arch_timer.h | 29 ++++--------------- arch/arm64/include/asm/common/arch_timer.h | 33 ++++++++++++++++++++++ arch/arm64/include/asm/vdso/gettimeofday.h | 7 +++-- 3 files changed, 42 insertions(+), 27 deletions(-) create mode 100644 arch/arm64/include/asm/common/arch_timer.h