Re: perf scripting

[Masami Hiramatsu]

(2010/09/16 21:08), Frederic Weisbecker wrote:
> (Sorry to answer that so late)
> 
> 
> On Sat, Aug 14, 2010 at 04:04:15PM -0400, Christoph Hellwig wrote:
>> On Fri, Jul 30, 2010 at 04:04:42PM +0200, Frederic Weisbecker wrote:
>>> I have the feeling you've made an ad-hoc post processing script that seems
>>> to rewrite all the format parsing, debugfs, stream handling, etc... we
>>> have that in perf tools already.
>>>
>>> May be you weren't aware of what we have in perf in terms of scripting support.
>>
>> Frederic, any chance you could help me getting a bit more familar with
>> the perf perl scripting.  I currently have a hacky little sequence that
>> I use to profile what callers generate XFS log traffic, and it like to
>> turn it into a script so that I can do a direct perf call to use it
>> to profile things without manual work, and generate nicer output.
>>
>> Currently it looks like this:
>>
>> perf probe --add xlog_sync
>>
>> perf record -g -e probe:xlog_sync -a -- <insert actualy workload here>
>>
>> then do
>>
>> perf report -n -g flat
>>
>> to get me the callchain in a readable format.
>>
>> Now what I'd really like is a perl script that can read a file like
>> latencytop.trans (or just has the information embedded) which contains
>> functions in the backtrace that we're interested in.
>>
>> E.g. one simple from the report command above may look like:
>>
>>                 xlog_sync
>> 		xlog_write
>> 		xlog_cil_push
>> 		_xfs_log_force
>> 		xfs_log_force
>> 		xfs_sync_data
>> 		xfs_quiesce_data
>> 		xfs_fs_sync_fs
>>
>> In which case I'm interested in xfs_log_force and xfs_fs_sync_fs.  So
>> the output of the perl script should looks something like:
>>
>>
>>   Samples	Caller
>> 	2	xfs_fs_sync_fs
>> 	1	xfs_file_fsync
>> 	1	xfs_commit_dummy_trans

BTW, if you want the caller for each call, you can do with perf probe

# perf probe --add 'xlog_sync caller=+0($stack)'

then, you can see the caller address in caller argument of
xlog_sync event record.


> Somehow, that's a kind of overview you can get with
> perf report, using the default fractal mode or the graph mode.
> Callers are sorted by hits in these modes (actually in raw mode too).
> 
> But it could be interesting to add the callchains as arguments to the
> perl/python scripting handlers for precise usecases.
> 
>  
>> Or if I have a way to parse the argument of the probe (in the worst case
>> I can replace it with a trace event if that makes it easier):
>>
>>   Samples	Flags		Callers
>> 	1	sync		xfs_fs_sync_fs
>> 	1			xfs_fs_sync_fs
>> 	1	sync		xfs_file_fsync
>> 	1	sync		xfs_commit_dummy_trans
> 
> 
> So for example that becomes an even more precise usecase.
> Currently the perf scripting engine doesn't give you access
> to the callchains of a trace sample. That would be a nice feature
> and would solve your problem.

AFAIK, perf perl script already supports getting arguments of
events. e.g.

sub probe::xlog_sync
{
    my ($event_name, $context, $common_cpu, $common_secs, $common_nsecs,
        $common_pid, $common_comm,
        $caller) = @_;

    if (!defined($caller_list{$caller})) {
         	$caller_list{$caller} = 0;
    }	
    $caller_list{$caller}++;
}

for count up caller address.
(However, perf perl currently doesn't have address-symbol translation
 function. )

If perf scripting supports calling perf internally for defining
new events for the script, it will be useful (from the viewpoint
of script packaging).

Thank you,

> 
> Tom, what do you think about that? This could be a special mode
> requested by the user, or something made automatically if callchains
> are present in samples. We could add a specific callchain extra
> argument to the generated scripting handlers, or this could
> be a generic extra dict argument that can contain whatever we want
> (perf sample headers, etc...), whatever extra data the user might
> request.
> 
> What do you think?
> 
> Thanks.
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