Re: [PATCH 6/6] perf, sort: Allow unique sorting instead of combining hist_entries

[Namhyung Kim <namhyung@kernel.org>]

Hi Don,

On Wed, 9 Apr 2014 09:57:06 -0400, Don Zickus wrote:
> On Wed, Apr 09, 2014 at 02:31:00PM +0900, Namhyung Kim wrote:
>> On Mon, 24 Mar 2014 15:34:36 -0400, Don Zickus wrote:
>> > The cache contention tools needs to keep all the perf records unique in order
>> > to properly parse all the data.  Currently add_hist_entry() will combine
>> > the duplicate record and add the weight/period to the existing record.
>> >
>> > This throws away the unique data the cache contention tool needs (mainly
>> > the data source).  Create a flag to force the records to stay unique.
>> 
>> No.  This is why I said you need to add 'mem' and 'snoop' sort keys into
>> the c2c tool.  This is not how sort works IMHO - if you need to make
>> samples unique let the sort key(s) distinguish them somehow, or you can
>> combine same samples (in terms of sort kes) and use the combined entry's
>> stat.nr_events and stat.period or weight.
>
> Ok.  I understand your point.  Perhaps this was my lack of fully
> understanding the sorting algorithm when I did this.  I can look into
> adding the 'mem' and 'snoop'.
>
> One concern I do have is we were caculating statistics based on the weight
> (mean, median, stddev).  I was afraid that combining the entries would
> throw off our calculations as we could no longer accurately determine them
> any more.  Is that true?

Yes, if you want to calculate the stats accurately, it needs to be done
when processing samples not hist_entries IMHO.

Thanks,
Namhyung