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From: Gang Li <ligang.bdlg@bytedance.com>
To: Steven Rostedt <rostedt@goodmis.org>,
	Axel Rasmussen <axelrasmussen@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>,
	Ingo Molnar <mingo@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	LKML <linux-kernel@vger.kernel.org>,
	Linux MM <linux-mm@kvack.org>
Subject: Re: [PATCH 3/3] mm: mmap_lock: add ip to mmap_lock tracepoints
Date: Fri, 20 Aug 2021 02:18:29 +0800	[thread overview]
Message-ID: <b0b30c3d-0fb8-7d29-2a60-0cce0309986b@bytedance.com> (raw)
In-Reply-To: <89c20b62-c0ab-3200-fb33-eb2058b7ba67@bytedance.com>

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.


  reply	other threads:[~2021-08-19 18:18 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-29  9:28 Gang Li
2021-07-29 17:33 ` Axel Rasmussen
2021-07-30  5:32   ` Gang Li
2021-07-30 20:03     ` Steven Rostedt
2021-08-02  2:44       ` Gang Li
2021-08-19 18:18         ` Gang Li [this message]
2021-08-31  3:24           ` Gang Li
2021-07-30  8:12   ` Vlastimil Babka

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