diff --git a/tools/arch/arm64/include/asm/barrier.h b/tools/arch/arm64/include/asm/barrier.h index 40bde6b23501..12835ea0e417 100644 --- a/tools/arch/arm64/include/asm/barrier.h +++ b/tools/arch/arm64/include/asm/barrier.h @@ -14,4 +14,74 @@ #define wmb() asm volatile("dmb ishst" ::: "memory") #define rmb() asm volatile("dmb ishld" ::: "memory") +#define smp_store_release(p, v) \ +do { \ + union { typeof(*p) __val; char __c[1]; } __u = \ + { .__val = (__force typeof(*p)) (v) }; \ + \ + switch (sizeof(*p)) { \ + case 1: \ + asm volatile ("stlrb %w1, %0" \ + : "=Q" (*p) \ + : "r" (*(__u8 *)__u.__c) \ + : "memory"); \ + break; \ + case 2: \ + asm volatile ("stlrh %w1, %0" \ + : "=Q" (*p) \ + : "r" (*(__u16 *)__u.__c) \ + : "memory"); \ + break; \ + case 4: \ + asm volatile ("stlr %w1, %0" \ + : "=Q" (*p) \ + : "r" (*(__u32 *)__u.__c) \ + : "memory"); \ + break; \ + case 8: \ + asm volatile ("stlr %1, %0" \ + : "=Q" (*p) \ + : "r" (*(__u64 *)__u.__c) \ + : "memory"); \ + break; \ + default: \ + /* Only to shut up gcc ... */ \ + mb(); \ + break; \ + } \ +} while (0) + +#define smp_load_acquire(p) \ +({ \ + union { typeof(*p) __val; char __c[1]; } __u; \ + \ + switch (sizeof(*p)) { \ + case 1: \ + asm volatile ("ldarb %w0, %1" \ + : "=r" (*(__u8 *)__u.__c) \ + : "Q" (*p) : "memory"); \ + break; \ + case 2: \ + asm volatile ("ldarh %w0, %1" \ + : "=r" (*(__u16 *)__u.__c) \ + : "Q" (*p) : "memory"); \ + break; \ + case 4: \ + asm volatile ("ldar %w0, %1" \ + : "=r" (*(__u32 *)__u.__c) \ + : "Q" (*p) : "memory"); \ + break; \ + case 8: \ + asm volatile ("ldar %0, %1" \ + : "=r" (*(__u64 *)__u.__c) \ + : "Q" (*p) : "memory"); \ + break; \ + default: \ + /* Only to shut up gcc ... */ \ + mb(); \ + break; \ + } \ + __u.__val; \ +}) + #endif /* _TOOLS_LINUX_ASM_AARCH64_BARRIER_H */ diff --git a/tools/arch/ia64/include/asm/barrier.h b/tools/arch/ia64/include/asm/barrier.h index d808ee0e77b5..4d471d9511a5 100644 --- a/tools/arch/ia64/include/asm/barrier.h +++ b/tools/arch/ia64/include/asm/barrier.h @@ -46,4 +46,17 @@ #define rmb() mb() #define wmb() mb() +#define smp_store_release(p, v) \ +do { \ + barrier(); \ + WRITE_ONCE(*p, v); \ +} while (0) + +#define smp_load_acquire(p) \ +({ \ + typeof(*p) ___p1 = READ_ONCE(*p); \ + barrier(); \ + ___p1; \ +}) + #endif /* _TOOLS_LINUX_ASM_IA64_BARRIER_H */ diff --git a/tools/arch/powerpc/include/asm/barrier.h b/tools/arch/powerpc/include/asm/barrier.h index a634da05bc97..905a2c66d96d 100644 --- a/tools/arch/powerpc/include/asm/barrier.h +++ b/tools/arch/powerpc/include/asm/barrier.h @@ -27,4 +27,20 @@ #define rmb() __asm__ __volatile__ ("sync" : : : "memory") #define wmb() __asm__ __volatile__ ("sync" : : : "memory") +#if defined(__powerpc64__) +#define smp_lwsync() __asm__ __volatile__ ("lwsync" : : : "memory") + +#define smp_store_release(p, v) \ +do { \ + smp_lwsync(); \ + WRITE_ONCE(*p, v); \ +} while (0) + +#define smp_load_acquire(p) \ +({ \ + typeof(*p) ___p1 = READ_ONCE(*p); \ + smp_lwsync(); \ + ___p1; \ +}) +#endif /* defined(__powerpc64__) */ #endif /* _TOOLS_LINUX_ASM_POWERPC_BARRIER_H */ diff --git a/tools/arch/s390/include/asm/barrier.h b/tools/arch/s390/include/asm/barrier.h index 5030c99f47d2..de362fa664d4 100644 --- a/tools/arch/s390/include/asm/barrier.h +++ b/tools/arch/s390/include/asm/barrier.h @@ -28,4 +28,17 @@ #define rmb() mb() #define wmb() mb() +#define smp_store_release(p, v) \ +do { \ + barrier(); \ + WRITE_ONCE(*p, v); \ +} while (0) + +#define smp_load_acquire(p) \ +({ \ + typeof(*p) ___p1 = READ_ONCE(*p); \ + barrier(); \ + ___p1; \ +}) + #endif /* __TOOLS_LIB_ASM_BARRIER_H */ diff --git a/tools/arch/sparc/include/asm/barrier_64.h b/tools/arch/sparc/include/asm/barrier_64.h index ba61344287d5..cfb0fdc8ccf0 100644 --- a/tools/arch/sparc/include/asm/barrier_64.h +++ b/tools/arch/sparc/include/asm/barrier_64.h @@ -40,4 +40,17 @@ do { __asm__ __volatile__("ba,pt %%xcc, 1f\n\t" \ #define rmb() __asm__ __volatile__("":::"memory") #define wmb() __asm__ __volatile__("":::"memory") +#define smp_store_release(p, v) \ +do { \ + barrier(); \ + WRITE_ONCE(*p, v); \ +} while (0) + +#define smp_load_acquire(p) \ +({ \ + typeof(*p) ___p1 = READ_ONCE(*p); \ + barrier(); \ + ___p1; \ +}) + #endif /* !(__TOOLS_LINUX_SPARC64_BARRIER_H) */ diff --git a/tools/arch/x86/include/asm/barrier.h b/tools/arch/x86/include/asm/barrier.h index 8774dee27471..58919868473c 100644 --- a/tools/arch/x86/include/asm/barrier.h +++ b/tools/arch/x86/include/asm/barrier.h @@ -26,4 +26,18 @@ #define wmb() asm volatile("sfence" ::: "memory") #endif +#if defined(__x86_64__) +#define smp_store_release(p, v) \ +do { \ + barrier(); \ + WRITE_ONCE(*p, v); \ +} while (0) + +#define smp_load_acquire(p) \ +({ \ + typeof(*p) ___p1 = READ_ONCE(*p); \ + barrier(); \ + ___p1; \ +}) +#endif /* defined(__x86_64__) */ #endif /* _TOOLS_LINUX_ASM_X86_BARRIER_H */ diff --git a/tools/include/asm/barrier.h b/tools/include/asm/barrier.h index 391d942536e5..8d378c57cb01 100644 --- a/tools/include/asm/barrier.h +++ b/tools/include/asm/barrier.h @@ -1,4 +1,5 @@ /* SPDX-License-Identifier: GPL-2.0 */ +#include #if defined(__i386__) || defined(__x86_64__) #include "../../arch/x86/include/asm/barrier.h" #elif defined(__arm__) @@ -26,3 +27,37 @@ #else #include #endif + +/* + * Generic fallback smp_*() definitions for archs that haven't + * been updated yet. + */ + +#ifndef smp_rmb +# define smp_rmb() rmb() +#endif + +#ifndef smp_wmb +# define smp_wmb() wmb() +#endif + +#ifndef smp_mb +# define smp_mb() mb() +#endif + +#ifndef smp_store_release +# define smp_store_release(p, v) \ +do { \ + smp_mb(); \ + WRITE_ONCE(*p, v); \ +} while (0) +#endif + +#ifndef smp_load_acquire +# define smp_load_acquire(p) \ +({ \ + typeof(*p) ___p1 = READ_ONCE(*p); \ + smp_mb(); \ + ___p1; \ +}) +#endif diff --git a/tools/include/linux/ring_buffer.h b/tools/include/linux/ring_buffer.h new file mode 100644 index 000000000000..9a083ae60473 --- /dev/null +++ b/tools/include/linux/ring_buffer.h @@ -0,0 +1,73 @@ +#ifndef _TOOLS_LINUX_RING_BUFFER_H_ +#define _TOOLS_LINUX_RING_BUFFER_H_ + +#include + +/* + * Contract with kernel for walking the perf ring buffer from + * user space requires the following barrier pairing (quote + * from kernel/events/ring_buffer.c): + * + * Since the mmap() consumer (userspace) can run on a + * different CPU: + * + * kernel user + * + * if (LOAD ->data_tail) { LOAD ->data_head + * (A) smp_rmb() (C) + * STORE $data LOAD $data + * smp_wmb() (B) smp_mb() (D) + * STORE ->data_head STORE ->data_tail + * } + * + * Where A pairs with D, and B pairs with C. + * + * In our case A is a control dependency that separates the + * load of the ->data_tail and the stores of $data. In case + * ->data_tail indicates there is no room in the buffer to + * store $data we do not. + * + * D needs to be a full barrier since it separates the data + * READ from the tail WRITE. + * + * For B a WMB is sufficient since it separates two WRITEs, + * and for C an RMB is sufficient since it separates two READs. + * + * Note, instead of B, C, D we could also use smp_store_release() + * in B and D as well as smp_load_acquire() in C. + * + * However, this optimization does not make sense for all kernel + * supported architectures since for a fair number it would + * resolve into READ_ONCE() + smp_mb() pair for smp_load_acquire(), + * and smp_mb() + WRITE_ONCE() pair for smp_store_release(). + * + * Thus for those smp_wmb() in B and smp_rmb() in C would still + * be less expensive. For the case of D this has either the same + * cost or is less expensive, for example, due to TSO x86 can + * avoid the CPU barrier entirely. + */ + +static inline u64 ring_buffer_read_head(struct perf_event_mmap_page *base) +{ +/* + * Architectures where smp_load_acquire() does not fallback to + * READ_ONCE() + smp_mb() pair. + */ +#if defined(__x86_64__) || defined(__aarch64__) || defined(__powerpc64__) || \ + defined(__ia64__) || defined(__sparc__) && defined(__arch64__) + return smp_load_acquire(&base->data_head); +#else + u64 head = READ_ONCE(base->data_head); + + smp_rmb(); + return head; +#endif +} + +static inline void ring_buffer_write_tail(struct perf_event_mmap_page *base, + u64 tail) +{ + smp_store_release(&base->data_tail, tail); +} + +#endif /* _TOOLS_LINUX_RING_BUFFER_H_ */ diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index bd71efcc53be..0c21355f04a7 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -27,6 +27,7 @@ #include #include #include +#include #include #include #include @@ -2418,13 +2419,12 @@ bpf_perf_event_read_simple(void *mem, unsigned long size, unsigned long page_size, void **buf, size_t *buf_len, bpf_perf_event_print_t fn, void *priv) { - volatile struct perf_event_mmap_page *header = mem; + struct perf_event_mmap_page *header = mem; + __u64 data_head = ring_buffer_read_head(header); __u64 data_tail = header->data_tail; - __u64 data_head = header->data_head; int ret = LIBBPF_PERF_EVENT_ERROR; void *base, *begin, *end; - asm volatile("" ::: "memory"); /* in real code it should be smp_rmb() */ if (data_head == data_tail) return LIBBPF_PERF_EVENT_CONT; @@ -2467,8 +2467,6 @@ bpf_perf_event_read_simple(void *mem, unsigned long size, data_tail += ehdr->size; } - __sync_synchronize(); /* smp_mb() */ - header->data_tail = data_tail; - + ring_buffer_write_tail(header, data_tail); return ret; } diff --git a/tools/perf/util/mmap.h b/tools/perf/util/mmap.h index 05a6d47c7956..8f6531fd4dad 100644 --- a/tools/perf/util/mmap.h +++ b/tools/perf/util/mmap.h @@ -4,7 +4,7 @@ #include #include #include -#include +#include #include #include "auxtrace.h" #include "event.h" @@ -71,21 +71,12 @@ void perf_mmap__consume(struct perf_mmap *map); static inline u64 perf_mmap__read_head(struct perf_mmap *mm) { - struct perf_event_mmap_page *pc = mm->base; - u64 head = READ_ONCE(pc->data_head); - rmb(); - return head; + return ring_buffer_read_head(mm->base); } static inline void perf_mmap__write_tail(struct perf_mmap *md, u64 tail) { - struct perf_event_mmap_page *pc = md->base; - - /* - * ensure all reads are done before we write the tail out. - */ - mb(); - pc->data_tail = tail; + ring_buffer_write_tail(md->base, tail); } union perf_event *perf_mmap__read_forward(struct perf_mmap *map);