[lttng-dev] [diamon-discuss] My experience on perf, CTF and TraceCompass, and some suggection.
alexmonthy at voxpopuli.im
Sat Feb 7 00:14:51 EST 2015
On 2015-02-06 10:13 PM, Wang Nan wrote:
>> I think such an approach could help in all 3 use cases you have presented. What do you think?
> Good to see you are looking at this problem.
> "Frequency analysis" you mentioned is a good viewpoint for finding outliner. However, it should not be the only one we consider. Could you please explain how "frequency analysis" can solve my first problem "finding the reason why most of CPUs are idle by matching syscalls events?"
> Thank you!
I was thinking of the automatic event matching, for example matching
syscall_entry_* events with their corresponding syscall_exit_*. This is
a pre-requisite of doing frequency analysis, but could be useful on its
own. (Re-reading myself now I notice I didn't mention event matching at
all, my bad!)
If I understand your first problem correctly, it boils down to wanting
to identify the system call that is ongoing when a CPU is idle. And this
is not straightforward, because the Select Next/Previous Event buttons
in the time graph views will stop at every state transition, like CPU
idle or IRQs, which are "in the way" of the system call entry event.
Now, what if we had a view that simply lists all the system calls in the
trace? Each row would contain the complete information of a system call,
so its start time (timestamp of the sys_entry event), end time
(timestamp of the sys_exit event), duration, name/id, arguments, return
And this view could be synchronized with the other ones, where clicking
on a row would bring you to the corresponding syscall_entry event. And
inversely, clicking on any timestamp would bring this view to the row
corresponding to the system call that was active at that time, if there
is one. I believe this could speed up your problem of identifying the
running system call for any arbitrary point in the trace.
Also, that view could be re-used for other types of intervals, like
IRQs, IO operations, and so on. And if the user sorts by the Duration
column, bam, they have a sorted list of the worst offenders for longer
system calls, IRQs, etc.
Would this be helpful?
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