Re: [PATCH 3/3] mm: mmap_lock: add ip to mmap_lock tracepoints

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On 8/2/21 10:44 AM, Gang Li wrote:
On 7/31/21 4:03 AM, Steven Rostedt wrote:
Yes, synthetic events are just like normal events, and have triggers,
stack traces, and do pretty much anything that another event can do.

I'm just finishing up a libtracfs called tracefs_sql() (hopefully
posting it today), that allows you to create a synthetic event via an
SQL statement. But I don't think this is what you are looking for.

What about using function tracing? Because the tracepoint is called
from __mmap_lock* helper functions that function tracer can see, you
can just do the following:

  # trace-cmd start -e mmap_lock -p function -l '__mmap_lock_*'
  # trace-cmd show
[..]
        trace-cmd-1840    [006] ....   194.576801: __mmap_lock_do_trace_start_locking <-do_user_addr_fault         trace-cmd-1840    [006] ...1   194.576805: mmap_lock_start_locking: mm=000000006515cb1f memcg_path=/user.slice/user-0.slice/session-2.scope write=false

Hi!

I find that sometimes the output data is out of order, which leads to inaccurate time stamps and make it hard to analyse.

node-953 [001] .... 203.823297: __mmap_lock_do_trace_start_locking <-do_user_addr_fault node-955 [002] .... 203.823297: __mmap_lock_do_trace_start_locking <-do_user_addr_fault node-956 [003] .... 203.823297: __mmap_lock_do_trace_start_locking <-do_user_addr_fault node-953 [001] .... 203.823297: mmap_lock_start_locking: mm=000000004395a005 memcg_path=/user.slice/user-0.slice/session-1.scope write=false ip=do_user_addr_fault+0x270/0x4d0 node-953 [001] .... 203.823298: __mmap_lock_do_trace_acquire_returned <-do_user_addr_fault

Is there any other way to collect ip in each event? It seems that adding "ip" fields is the only way to do this accurately and effectively.





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