> -----Original Message----- > From: neeraju=codeaurora.org@xxxxxxxxxxxxxxxxx <neeraju=codeaurora.org@xxxxxxxxxxxxxxxxx> > Neeraj Upadhyay > Sent: Wednesday, February 24, 2021 6:19 PM > > 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 ? I agree. It is good to be located before printing console message. I'll revise the patch. Or, should I make a patch with start-end pair? Thanks, Sangmoon > > > 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 > > > > -- > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a > member of the Code Aurora Forum, hosted by The Linux Foundation
