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SubjectRe: [rfd] function-graph augmentation

* Peter Zijlstra <peterz@infradead.org> wrote:

> Hi,
>
> I was thinking how best to augment the function graph tracer
> with various information. It seemed useful to add
> argument/return tracer entries which, when found after a
> function entry, or function exit entry would be rendered in
> the trace.
>
> So supposing something like;
>
> 3) | handle_mm_fault() {
> 3) | count_vm_event() {
> 3) 0.243 us | test_ti_thread_flag();
> 3) 0.754 us | }
> 3) 0.249 us | pud_alloc();
> 3) 0.251 us | pmd_alloc();
> 3) | __do_fault() {
> 3) | filemap_fault() {
> 3) | find_lock_page() {
> 3) | find_get_page() {
> 3) 0.248 us | test_ti_thread_flag();
> 3) 0.844 us | }
> 3) 1.341 us | }
> 3) 1.837 us | }
> 3) 0.275 us | _spin_lock();
> 3) 0.257 us | page_add_file_rmap();
> 3) 0.233 us | native_set_pte_at();
> 3) | _spin_unlock() {
> 3) 0.248 us | test_ti_thread_flag();
> 3) 0.742 us | }
> 3) | unlock_page() {
> 3) 0.243 us | page_waitqueue();
> 3) 0.237 us | __wake_up_bit();
> 3) 1.209 us | }
> 3) 6.274 us | }
> 3) 8.806 us | }
>
> Say we found:
>
> trace_graph_entry -- handle_mm_fault()
> trace_func_arg -- address:0xffffffff
> trace_func_arg -- write_access:1
>
> We'd render:
>
> 3) | handle_mm_fault(.address=0xffffffff, .write_access=1) {
>
> trace_graph_return -- handle_mm_fault()
> trace_func_ret -- 2
>
> We'd render:
>
> 3) 8.806 us | } = 2
>
> Then we can register with tracepoints inside functions to add
> these generic trace_func_arg/_ret entries to augment the graph
> (and or function) tracer.
>
> Does that make sense?

Yeah, it looks really nice that way.

Ingo


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