RFE: perf lock contention --bpf on an RT kernel
From: Arnaldo Carvalho de Melo
Date: Thu Aug 17 2023 - 09:58:18 EST
Hi Namhyung, I noticed this when trying to use the BPF mode of perf lock
contention on an RT kernel:
[root@nine perf-tools-next]# perf lock contention -ba
libbpf: prog 'contention_begin': BPF program load failed: Invalid argument
libbpf: prog 'contention_begin': -- BEGIN PROG LOAD LOG --
R1 type=ctx expected=fp
0: R1=ctx(off=0,imm=0) R10=fp0
; int contention_begin(u64 *ctx)
0: (bf) r7 = r1 ; R1=ctx(off=0,imm=0) R7_w=ctx(off=0,imm=0)
; if (!enabled || !can_record(ctx))
1: (18) r1 = 0xffffc077c0322000 ; R1_w=map_value(off=0,ks=4,vs=60,imm=0)
3: (61) r1 = *(u32 *)(r1 +0) ; R1_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; if (!enabled || !can_record(ctx))
4: (15) if r1 == 0x0 goto pc+209 ; R1_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; if (has_cpu) {
5: (18) r1 = 0xffffc077c0322028 ; R1_w=map_value(off=40,ks=4,vs=60,imm=0)
7: (61) r1 = *(u32 *)(r1 +0) ; R1_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; if (has_cpu) {
8: (15) if r1 == 0x0 goto pc+8 ; R1_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; __u32 cpu = bpf_get_smp_processor_id();
9: (85) call bpf_get_smp_processor_id#8 ; R0=scalar()
; __u32 cpu = bpf_get_smp_processor_id();
10: (63) *(u32 *)(r10 -32) = r0 ; R0=scalar() R10=fp0 fp-32=????mmmm
11: (bf) r2 = r10 ; R2_w=fp0 R10=fp0
; __u32 cpu = bpf_get_smp_processor_id();
12: (07) r2 += -32 ; R2_w=fp-32
; ok = bpf_map_lookup_elem(&cpu_filter, &cpu);
13: (18) r1 = 0xffff9f260667b800 ; R1_w=map_ptr(off=0,ks=4,vs=1,imm=0)
15: (85) call bpf_map_lookup_elem#1 ; R0_w=map_value_or_null(id=1,off=0,ks=4,vs=1,imm=0)
16: (15) if r0 == 0x0 goto pc+197 ; R0_w=map_value(off=0,ks=4,vs=1,imm=0)
; if (has_task) {
17: (18) r1 = 0xffffc077c032202c ; R1_w=map_value(off=44,ks=4,vs=60,imm=0)
19: (61) r1 = *(u32 *)(r1 +0) ; R1=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; if (has_task) {
20: (15) if r1 == 0x0 goto pc+8 ; R1=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; __u32 pid = bpf_get_current_pid_tgid();
21: (85) call bpf_get_current_pid_tgid#14 ; R0_w=scalar()
; __u32 pid = bpf_get_current_pid_tgid();
22: (63) *(u32 *)(r10 -32) = r0 ; R0_w=scalar() R10=fp0 fp-32=????mmmm
23: (bf) r2 = r10 ; R2_w=fp0 R10=fp0
; __u32 pid = bpf_get_current_pid_tgid();
24: (07) r2 += -32 ; R2_w=fp-32
; ok = bpf_map_lookup_elem(&task_filter, &pid);
25: (18) r1 = 0xffff9f260667b400 ; R1_w=map_ptr(off=0,ks=4,vs=1,imm=0)
27: (85) call bpf_map_lookup_elem#1 ; R0_w=map_value_or_null(id=2,off=0,ks=4,vs=1,imm=0)
28: (15) if r0 == 0x0 goto pc+185 ; R0_w=map_value(off=0,ks=4,vs=1,imm=0)
; if (has_type) {
29: (18) r1 = 0xffffc077c0322030 ; R1_w=map_value(off=48,ks=4,vs=60,imm=0)
31: (61) r1 = *(u32 *)(r1 +0) ; R1_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; if (has_type) {
32: (15) if r1 == 0x0 goto pc+8 ; R1_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; __u32 flags = (__u32)ctx[1];
33: (79) r1 = *(u64 *)(r7 +8) ; R1_w=scalar() R7=ctx(off=0,imm=0)
; __u32 flags = (__u32)ctx[1];
34: (63) *(u32 *)(r10 -32) = r1 ; R1_w=scalar() R10=fp0 fp-32=????mmmm
35: (bf) r2 = r10 ; R2_w=fp0 R10=fp0
; __u32 flags = (__u32)ctx[1];
36: (07) r2 += -32 ; R2_w=fp-32
; ok = bpf_map_lookup_elem(&type_filter, &flags);
37: (18) r1 = 0xffff9f260667b000 ; R1_w=map_ptr(off=0,ks=4,vs=1,imm=0)
39: (85) call bpf_map_lookup_elem#1 ; R0=map_value_or_null(id=3,off=0,ks=4,vs=1,imm=0)
40: (15) if r0 == 0x0 goto pc+173 ; R0=map_value(off=0,ks=4,vs=1,imm=0)
; if (has_addr) {
41: (18) r1 = 0xffffc077c0322034 ; R1_w=map_value(off=52,ks=4,vs=60,imm=0)
43: (61) r1 = *(u32 *)(r1 +0) ; R1_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; if (has_addr) {
44: (15) if r1 == 0x0 goto pc+8 ; R1_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; __u64 addr = ctx[0];
45: (79) r1 = *(u64 *)(r7 +0) ; R1_w=scalar() R7=ctx(off=0,imm=0)
; __u64 addr = ctx[0];
46: (7b) *(u64 *)(r10 -32) = r1 ; R1_w=scalar() R10=fp0 fp-32_w=mmmmmmmm
47: (bf) r2 = r10 ; R2_w=fp0 R10=fp0
; __u64 addr = ctx[0];
48: (07) r2 += -32 ; R2_w=fp-32
; ok = bpf_map_lookup_elem(&addr_filter, &addr);
49: (18) r1 = 0xffff9f260667f400 ; R1_w=map_ptr(off=0,ks=8,vs=1,imm=0)
51: (85) call bpf_map_lookup_elem#1 ; R0=map_value_or_null(id=4,off=0,ks=8,vs=1,imm=0)
; if (!enabled || !can_record(ctx))
52: (15) if r0 == 0x0 goto pc+161 ; R0=map_value(off=0,ks=8,vs=1,imm=0)
; pid = bpf_get_current_pid_tgid();
53: (85) call bpf_get_current_pid_tgid#14 ; R0_w=scalar()
; pid = bpf_get_current_pid_tgid();
54: (63) *(u32 *)(r10 -8) = r0 ; R0_w=scalar() R10=fp0 fp-8=????mmmm
55: (bf) r2 = r10 ; R2_w=fp0 R10=fp0
; pid = bpf_get_current_pid_tgid();
56: (07) r2 += -8 ; R2_w=fp-8
; pelem = bpf_map_lookup_elem(&tstamp, &pid);
57: (18) r1 = 0xffff9f260667a800 ; R1_w=map_ptr(off=0,ks=4,vs=24,imm=0)
59: (85) call bpf_map_lookup_elem#1 ; R0_w=map_value_or_null(id=5,off=0,ks=4,vs=24,imm=0)
60: (bf) r6 = r0 ; R0=map_value_or_null(id=5,off=0,ks=4,vs=24,imm=0) R6=map_value_or_null(id=5,off=0,ks=4,vs=24,imm=0)
; if (pelem && pelem->lock)
61: (15) if r6 == 0x0 goto pc+32 ; R6=map_value(off=0,ks=4,vs=24,imm=0)
; if (pelem && pelem->lock)
62: (79) r1 = *(u64 *)(r6 +8) ; R1_w=scalar() R6=map_value(off=0,ks=4,vs=24,imm=0)
; if (pelem && pelem->lock)
63: (15) if r1 == 0x0 goto pc+1 65: R0=map_value(off=0,ks=4,vs=24,imm=0) R1_w=0 R6=map_value(off=0,ks=4,vs=24,imm=0) R7=ctx(off=0,imm=0) R10=fp0 fp-8=????mmmm fp-32=mmmmmmmm
; pelem->timestamp = bpf_ktime_get_ns();
65: (85) call bpf_ktime_get_ns#5 ; R0_w=scalar()
; pelem->timestamp = bpf_ktime_get_ns();
66: (7b) *(u64 *)(r6 +0) = r0 ; R0_w=scalar() R6=map_value(off=0,ks=4,vs=24,imm=0)
; pelem->lock = (__u64)ctx[0];
67: (79) r3 = *(u64 *)(r7 +0) ; R3_w=scalar() R7=ctx(off=0,imm=0)
; pelem->lock = (__u64)ctx[0];
68: (7b) *(u64 *)(r6 +8) = r3 ; R3_w=scalar() R6=map_value(off=0,ks=4,vs=24,imm=0)
; pelem->flags = (__u32)ctx[1];
69: (79) r1 = *(u64 *)(r7 +8) ; R1_w=scalar() R7=ctx(off=0,imm=0)
; pelem->flags = (__u32)ctx[1];
70: (63) *(u32 *)(r6 +16) = r1 ; R1_w=scalar() R6=map_value(off=0,ks=4,vs=24,imm=0)
; if (needs_callstack) {
71: (18) r2 = 0xffffc077c0322008 ; R2_w=map_value(off=8,ks=4,vs=60,imm=0)
73: (61) r2 = *(u32 *)(r2 +0) ; R2=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; if (needs_callstack) {
74: (15) if r2 == 0x0 goto pc+43 118: R0=scalar() R1=scalar() R2=0 R3=scalar() R6=map_value(off=0,ks=4,vs=24,imm=0) R7=ctx(off=0,imm=0) R10=fp0 fp-8=????mmmm fp-32=mmmmmmmm
; } else if (aggr_mode == LOCK_AGGR_TASK) {
118: (18) r2 = 0xffffc077c0322014 ; R2_w=map_value(off=20,ks=4,vs=60,imm=0)
120: (61) r2 = *(u32 *)(r2 +0) ; R2_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; } else if (aggr_mode == LOCK_AGGR_TASK) {
121: (55) if r2 != 0x1 goto pc+92 ; R2_w=1
; if (lock_owner) {
122: (18) r2 = 0xffffc077c0322018 ; R2_w=map_value(off=24,ks=4,vs=60,imm=0)
124: (61) r2 = *(u32 *)(r2 +0) ; R2=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; if (lock_owner) {
125: (15) if r2 == 0x0 goto pc+34 ; R2=scalar(umax=4294967295,var_off=(0x0; 0xffffffff))
; if (flags & LCB_F_MUTEX) {
126: (bf) r2 = r1 ; R1=scalar(id=6) R2_w=scalar(id=6)
127: (57) r2 &= 32 ; R2_w=scalar(umax=32,var_off=(0x0; 0x20))
; if (flags & LCB_F_MUTEX) {
128: (15) if r2 == 0x0 goto pc+2 ; R2_w=scalar(umax=32,var_off=(0x0; 0x20))
129: <invalid CO-RE relocation>
failed to resolve CO-RE relocation <byte_off> [47] struct mutex.owner.counter (0:0:0 @ offset 0)
processed 95 insns (limit 1000000) max_states_per_insn 0 total_states 10 peak_states 10 mark_read 4
-- END PROG LOAD LOG --
libbpf: prog 'contention_begin': failed to load: -22
libbpf: failed to load object 'lock_contention_bpf'
libbpf: failed to load BPF skeleton 'lock_contention_bpf': -22
Failed to load lock-contention BPF skeleton
lock contention BPF setup failed
[root@nine perf-tools-next]# uname -r
5.14.0-284.18.1.rt14.303.el9_2.x86_64
[root@nine perf-tools-next]# pahole mutex
struct mutex {
struct rt_mutex_base rtmutex; /* 0 32 */
/* size: 32, cachelines: 1, members: 1 */
/* last cacheline: 32 bytes */
};
[root@nine perf-tools-next]# pahole -E mutex
struct mutex {
struct rt_mutex_base {
/* typedef raw_spinlock_t */ struct raw_spinlock {
/* typedef arch_spinlock_t */ struct qspinlock {
union {
/* typedef atomic_t */ struct {
int counter; /* 0 4 */
} val; /* 0 4 */
struct {
/* typedef u8 -> __u8 */ unsigned char locked; /* 0 1 */
/* typedef u8 -> __u8 */ unsigned char pending; /* 1 1 */
}; /* 0 2 */
struct {
/* typedef u16 -> __u16 */ short unsigned int locked_pending; /* 0 2 */
/* typedef u16 -> __u16 */ short unsigned int tail; /* 2 2 */
}; /* 0 4 */
}; /* 0 4 */
} raw_lock; /* 0 4 */
} wait_lock; /* 0 4 */
/* XXX 4 bytes hole, try to pack */
struct rb_root_cached {
struct rb_root {
struct rb_node * rb_node; /* 8 8 */
}rb_root; /* 8 8 */
struct rb_node * rb_leftmost; /* 16 8 */
}waiters; /* 8 16 */
struct task_struct * owner; /* 24 8 */
}rtmutex; /* 0 32 */
/* size: 32, cachelines: 1, members: 1 */
/* last cacheline: 32 bytes */
};
[root@nine perf-tools-next]# uname -r
5.14.0-284.18.1.rt14.303.el9_2.x86_64
[root@nine perf-tools-next]#
So we need some extra logic to get at the mutex owner...
[root@nine perf-tools-next]# ls -la /sys/kernel/debug/tracing/events/lock/
contention_begin/ contention_end/ enable filter
[root@nine perf-tools-next]# ls -la /sys/kernel/debug/tracing/events/lock/
total 0
drwxr-xr-x. 4 root root 0 Aug 17 08:44 .
drwxr-xr-x. 114 root root 0 Aug 17 08:45 ..
drwxr-xr-x. 2 root root 0 Aug 17 08:44 contention_begin
drwxr-xr-x. 2 root root 0 Aug 17 08:44 contention_end
-rw-r-----. 1 root root 0 Aug 17 08:44 enable
-rw-r-----. 1 root root 0 Aug 17 08:44 filter
[root@nine perf-tools-next]#
I tried up to now the following patch, it loads, but produces no output
:-\
diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c
index 8d3cfbb3cc65..8b65391401a5 100644
--- a/tools/perf/util/bpf_skel/lock_contention.bpf.c
+++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c
@@ -100,6 +100,18 @@ struct rw_semaphore___new {
atomic_long_t owner;
} __attribute__((preserve_access_index));
+struct rw_semaphore___rt {
+ struct rwbase_rt {
+ struct rt_mutex_base {
+ struct task_struct *owner;
+ } rtmutex;
+ } rwbase;
+} __attribute__((preserve_access_index));
+
+struct mutex___rt {
+ struct rt_mutex_base rtmutex;
+} __attribute__((preserve_access_index));
+
struct mm_struct___old {
struct rw_semaphore mmap_sem;
} __attribute__((preserve_access_index));
@@ -202,8 +214,19 @@ static inline struct task_struct *get_lock_owner(__u64 lock, __u32 flags)
__u64 owner = 0;
if (flags & LCB_F_MUTEX) {
+#if __has_builtin(__builtin_preserve_type_info) && __clang_major__ >= 15
+ if (bpf_core_type_matches(struct mutex___rt)) {
+ struct mutex___rt *mutex = (void *)lock;
+ owner = (unsigned long)BPF_CORE_READ(mutex, rtmutex.owner);
+ } else if (bpf_core_type_matches(struct mutex)) {
+ struct mutex *mutex = (void *)lock;
+ owner = BPF_CORE_READ(mutex, owner.counter);
+ }
+#else
+ /* assume non-RT struct */
struct mutex *mutex = (void *)lock;
owner = BPF_CORE_READ(mutex, owner.counter);
+#endif
} else if (flags == LCB_F_READ || flags == LCB_F_WRITE) {
/*
* Support for the BPF_TYPE_MATCHES argument to the
@@ -218,6 +241,9 @@ static inline struct task_struct *get_lock_owner(__u64 lock, __u32 flags)
} else if (bpf_core_type_matches(struct rw_semaphore___new)) {
struct rw_semaphore___new *rwsem = (void *)lock;
owner = BPF_CORE_READ(rwsem, owner.counter);
+ } else if (bpf_core_type_matches(struct rw_semaphore___rt)) {
+ struct rw_semaphore___rt *rwsem = (void *)lock;
+ owner = (unsigned long)BPF_CORE_READ(rwsem, rwbase.rtmutex.owner);
}
#else
/* assume new struct */