linux-kernel - Re: [PATCH RFC 1/2] perf tools: Support single perf.data file directory

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Date:   Tue, 24 Sep 2019 13:12:32 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 1/2] perf tools: Support single perf.data file
 directory

On Tue, Sep 24, 2019 at 12:12:25PM +0300, Adrian Hunter wrote:
> On 24/09/19 12:34 AM, Jiri Olsa wrote:
> > On Mon, Sep 16, 2019 at 11:56:45AM +0300, Adrian Hunter wrote:
> >> Support directory output that contains a regular perf.data file. This is
> >> preparation for adding support for putting a copy of /proc/kcore in that
> >> directory.
> >>
> >> Distinguish the multiple file case from the regular (single) perf.data file
> >> case by adding data->is_multi_file.
> > 
> > SNIP
> > 
> >>  static int open_file_read(struct perf_data *data)
> >>  {
> >>  	struct stat st;
> >> @@ -302,12 +312,17 @@ static int open_dir(struct perf_data *data)
> >>  {
> >>  	int ret;
> >>  
> >> -	/*
> >> -	 * So far we open only the header, so we can read the data version and
> >> -	 * layout.
> >> -	 */
> >> -	if (asprintf(&data->file.path, "%s/header", data->path) < 0)
> >> -		return -1;
> >> +	if (perf_data__is_multi_file(data)) {
> >> +		/*
> >> +		 * So far we open only the header, so we can read the data version and
> >> +		 * layout.
> >> +		 */
> >> +		if (asprintf(&data->file.path, "%s/header", data->path) < 0)
> >> +			return -1;
> >> +	} else {
> >> +		if (asprintf(&data->file.path, "%s/perf.data", data->path) < 0)
> >> +			return -1;
> >> +	}
> > 
> 
> Thanks for replying :-)
> 
> > first, please note that there's support for perf.data directory code,
> > but it's not been enabled yet, so we can do any changes there without
> > breaking existing users
> > 
> > currently the logic is prepared to have perf.data DIR_FORMAT feature
> > to define the layout of the directory
> > 
> > it'd be great to have just single point where we get directory layout,
> > not checking on files names first and checking on DIR_FORMAT later
> 
> Ok, but what are you suggesting?  Naming the data file "header" seems a bit
> counter-intuitive in this case.

don't know ;-)

but I'd like to have one way of finding out the directory layout

the code for threaded record uses DIR_FORMAT feature value
to ensure the directory contains the expected files, which
is data file with 'data.<cpu>' name for every cpu

> 
> > 
> > also the kcore will be beneficial for other layouts,
> > so would be great to make it somehow optional/switchable
> 
> In these patches it is, because it is not related to the DIR_FORMAT.
> 
> > one of the options could be to have DIR_FORMAT feature as the source
> > of directory layout and it'd have bitmask of files/dirs (like kcore_dir)
> > available in the directory
> 
> Is there an advantage to making optional files/dirs part of the format?
> i.e. if they are there, use them otherwise don't.

ok, that might work, but please make that somehow explicit/visible
what files/directories are possible in the directory, so we could
easily see them and add new ones

jirka