From c66a36af7ba3a628453da1d91f42ee64fb36ea5a Mon Sep 17 00:00:00 2001 From: Namhyung Kim Date: Fri, 18 Nov 2022 11:01:09 -0800 Subject: [PATCH] perf lock contention: Do not use BPF task local storage It caused some troubles when a lock inside kmalloc is contended because task local storage would allocate memory using kmalloc. It'd create a recusion and even crash in my system. There could be a couple of workarounds but I think the simplest one is to use a pre-allocated hash map. We could fix the task local storage to use the safe BPF allocator, but it takes time so let's change this until it happens actually. Signed-off-by: Namhyung Kim Acked-by: Martin KaFai Lau Cc: Adrian Hunter Cc: Blake Jones Cc: Chris Li Cc: Ian Rogers Cc: Ingo Molnar Cc: Jiri Olsa Cc: Peter Zijlstra Cc: Song Liu Cc: bpf@vger.kernel.org Link: https://lore.kernel.org/r/20221118190109.1512674-1-namhyung@kernel.org Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/bpf_lock_contention.c | 1 + tools/perf/util/bpf_skel/lock_contention.bpf.c | 34 +++++++++++++++++--------- 2 files changed, 23 insertions(+), 12 deletions(-) diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c index 0deec11..4db9ad3 100644 --- a/tools/perf/util/bpf_lock_contention.c +++ b/tools/perf/util/bpf_lock_contention.c @@ -39,6 +39,7 @@ int lock_contention_prepare(struct lock_contention *con) bpf_map__set_value_size(skel->maps.stacks, con->max_stack * sizeof(u64)); bpf_map__set_max_entries(skel->maps.stacks, con->map_nr_entries); bpf_map__set_max_entries(skel->maps.lock_stat, con->map_nr_entries); + bpf_map__set_max_entries(skel->maps.tstamp, con->map_nr_entries); if (target__has_cpu(target)) ncpus = perf_cpu_map__nr(evlist->core.user_requested_cpus); diff --git a/tools/perf/util/bpf_skel/lock_contention.bpf.c b/tools/perf/util/bpf_skel/lock_contention.bpf.c index 1bb8628..9681cb5 100644 --- a/tools/perf/util/bpf_skel/lock_contention.bpf.c +++ b/tools/perf/util/bpf_skel/lock_contention.bpf.c @@ -40,10 +40,10 @@ struct { /* maintain timestamp at the beginning of contention */ struct { - __uint(type, BPF_MAP_TYPE_TASK_STORAGE); - __uint(map_flags, BPF_F_NO_PREALLOC); + __uint(type, BPF_MAP_TYPE_HASH); __type(key, int); __type(value, struct tstamp_data); + __uint(max_entries, MAX_ENTRIES); } tstamp SEC(".maps"); /* actual lock contention statistics */ @@ -103,18 +103,28 @@ static inline int can_record(void) SEC("tp_btf/contention_begin") int contention_begin(u64 *ctx) { - struct task_struct *curr; + __u32 pid; struct tstamp_data *pelem; if (!enabled || !can_record()) return 0; - curr = bpf_get_current_task_btf(); - pelem = bpf_task_storage_get(&tstamp, curr, NULL, - BPF_LOCAL_STORAGE_GET_F_CREATE); - if (!pelem || pelem->lock) + pid = bpf_get_current_pid_tgid(); + pelem = bpf_map_lookup_elem(&tstamp, &pid); + if (pelem && pelem->lock) return 0; + if (pelem == NULL) { + struct tstamp_data zero = {}; + + bpf_map_update_elem(&tstamp, &pid, &zero, BPF_ANY); + pelem = bpf_map_lookup_elem(&tstamp, &pid); + if (pelem == NULL) { + lost++; + return 0; + } + } + pelem->timestamp = bpf_ktime_get_ns(); pelem->lock = (__u64)ctx[0]; pelem->flags = (__u32)ctx[1]; @@ -128,7 +138,7 @@ int contention_begin(u64 *ctx) SEC("tp_btf/contention_end") int contention_end(u64 *ctx) { - struct task_struct *curr; + __u32 pid; struct tstamp_data *pelem; struct contention_key key; struct contention_data *data; @@ -137,8 +147,8 @@ int contention_end(u64 *ctx) if (!enabled) return 0; - curr = bpf_get_current_task_btf(); - pelem = bpf_task_storage_get(&tstamp, curr, NULL, 0); + pid = bpf_get_current_pid_tgid(); + pelem = bpf_map_lookup_elem(&tstamp, &pid); if (!pelem || pelem->lock != ctx[0]) return 0; @@ -156,7 +166,7 @@ int contention_end(u64 *ctx) }; bpf_map_update_elem(&lock_stat, &key, &first, BPF_NOEXIST); - pelem->lock = 0; + bpf_map_delete_elem(&tstamp, &pid); return 0; } @@ -169,7 +179,7 @@ int contention_end(u64 *ctx) if (data->min_time > duration) data->min_time = duration; - pelem->lock = 0; + bpf_map_delete_elem(&tstamp, &pid); return 0; } -- 2.7.4