Messages in this thread Patch in this message | | | Date | Mon, 17 Jun 2013 11:41:46 +0800 | From | "zhangwei(Jovi)" <> | Subject | Re: [PATCH 1/3] tracing/kprobes: Avoid perf_trace_buf_*() if ->perf_events is empty |
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On 2013/6/17 1:21, Oleg Nesterov wrote: > perf_trace_buf_prepare() + perf_trace_buf_submit() make no sense > if this task/CPU has no active counters. Change kprobe_perf_func() > and kretprobe_perf_func() to check call->perf_events beforehand > and return if this list is empty. > > For example, "perf record -e some_probe -p1". Only /sbin/init will > report, all other threads which hit the same probe will do > perf_trace_buf_prepare/perf_trace_buf_submit just to realize that > nobody wants perf_swevent_event(). > > Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Good point, I think we also need to change other places in below patch.
After applied the patch, perf_tp_event() function call reduced a lots when using task based perf tracing.
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tracing: Avoid perf_trace_buf_*() if ->perf_events is empty
Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@huawei.com> --- include/trace/ftrace.h | 5 ++++- kernel/trace/trace_syscalls.c | 10 ++++++++-- 2 files changed, 12 insertions(+), 3 deletions(-)
diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h index 19edd7f..5d340f5 100644 --- a/include/trace/ftrace.h +++ b/include/trace/ftrace.h @@ -659,6 +659,10 @@ perf_trace_##call(void *__data, proto) \ int __data_size; \ int rctx; \ \ + head = this_cpu_ptr(event_call->perf_events); \ + if (hlist_empty(head)) \ + return; \ + \ perf_fetch_caller_regs(&__regs); \ \ __data_size = ftrace_get_offsets_##call(&__data_offsets, args); \ @@ -679,7 +683,6 @@ perf_trace_##call(void *__data, proto) \ \ { assign; } \ \ - head = this_cpu_ptr(event_call->perf_events); \ perf_trace_buf_submit(entry, __entry_size, rctx, __addr, \ __count, &__regs, head, __task); \ } diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c index 8f2ac73..28debf4 100644 --- a/kernel/trace/trace_syscalls.c +++ b/kernel/trace/trace_syscalls.c @@ -553,6 +553,10 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id) if (!sys_data) return;
+ head = this_cpu_ptr(sys_data->enter_event->perf_events); + if (hlist_empty(head)) + return; + /* get the size after alignment with the u32 buffer size field */ size = sizeof(unsigned long) * sys_data->nb_args + sizeof(*rec); size = ALIGN(size + sizeof(u32), sizeof(u64)); @@ -571,7 +575,6 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id) syscall_get_arguments(current, regs, 0, sys_data->nb_args, (unsigned long *)&rec->args);
- head = this_cpu_ptr(sys_data->enter_event->perf_events); perf_trace_buf_submit(rec, size, rctx, 0, 1, regs, head, NULL); }
@@ -629,6 +632,10 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret) if (!sys_data) return;
+ head = this_cpu_ptr(sys_data->exit_event->perf_events); + if (hlist_empty(head)) + return; + /* We can probably do that at build time */ size = ALIGN(sizeof(*rec) + sizeof(u32), sizeof(u64)); size -= sizeof(u32); @@ -649,7 +656,6 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret) rec->nr = syscall_nr; rec->ret = syscall_get_return_value(current, regs);
- head = this_cpu_ptr(sys_data->exit_event->perf_events); perf_trace_buf_submit(rec, size, rctx, 0, 1, regs, head, NULL); }
-- 1.7.9.7
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