Hi Sangmoon,
On 2/22/2021 1:55 PM, Sangmoon Kim wrote:
-----Original Message-----
From: Paul E. McKenney <paulmck@xxxxxxxxxx>
Sent: Friday, February 19, 2021 3:59 AM
On Thu, Feb 18, 2021 at 01:24:16PM -0500, Steven Rostedt wrote:
On Thu, 18 Feb 2021 09:00:12 -0800
"Paul E. McKenney" <paulmck@xxxxxxxxxx> wrote:
OK, I will bite. ;-)
Do I turn into a wearwolf?
Maybe even a wash-n-wear wolf. ;-)
Can the saving of console into trace buffers be easily enabled and
disabled within the code?
Well, we do have this for ftrace:
echo 'enable_event:printk:console' > events/rcu/rcu_stall_warning/trigger
Would enable the printk console to be traced to the ring buffer once the
stall is triggered, and not before hand.
If so, does enabling and disabling nest?
It has a disable as well, but unfortunately its global and does not nest.
We could always implement a percpu trigger that can nest though.
So Sangmoon could have a module react to an RCU CPU stall warning
tracepoint by turning on tracing of console messages. If there was a
start-stop pair of RCU CPU stall warning tracepoints, he could turn it
off as well.
Not sure if that is what Sangmoon is looking for, but it is a possibility.
Thanx, Paul
Thank you. I'm learning the new things through this review.
Copying console messages is not really necessary to me. I wanted to say
this tracepoint can also be used in such way for debugging purpose.
In case we want to use this trace event, to capture RCU stall
information, which comes on console, into trace buffers; why not have
these events at the start of the functions like print_other_cpu_stall(),
print_cpu_stall() rather than at the end ?
Thanks
Neeraj
What I need is that a module records the stall happening and report the
stall event when kernel panic occurred. Of course, there is no detailed
information there, but it helps developers to recognize that the stall
has occurred in the system.
The usage scenario is as follows.
There is a kernel module for debugging.
The module registers a probe function using register_trace_rcu_stall_warning().
When a stall warning event occurs, the module records the event into its own buffer.
When a kernel panic occurs, the developers can see the report generated
by the module and can also see the buffer of the module directly through Ramdump.
Thanks,
Sangmoon
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