Re: [RFC PATCH v3 12/14] perf metricgroup: order event groups by size

[Andi Kleen]

On Thu, May 07, 2020 at 10:36:27PM -0700, Ian Rogers wrote:
> When adding event groups to the group list, insert them in size order.
> This performs an insertion sort on the group list. By placing the
> largest groups at the front of the group list it is possible to see if a
> larger group contains the same events as a later group. This can make
> the later group redundant - it can reuse the events from the large group.
> A later patch will add this sharing.

I'm not sure if size is that great an heuristic. The dedup algorithm should
work in any case even if you don't order by size, right?

I suppose in theory some kind of topological sort would be better.

-Andi
> 
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
>  tools/perf/util/metricgroup.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/metricgroup.c b/tools/perf/util/metricgroup.c
> index 2a6456fa178b..69fbff47089f 100644
> --- a/tools/perf/util/metricgroup.c
> +++ b/tools/perf/util/metricgroup.c
> @@ -520,7 +520,21 @@ static int __metricgroup__add_metric(struct list_head *group_list,
>  		return -EINVAL;
>  	}
>  
> -	list_add_tail(&eg->nd, group_list);
> +	if (list_empty(group_list))
> +		list_add(&eg->nd, group_list);
> +	else {
> +		struct list_head *pos;
> +
> +		/* Place the largest groups at the front. */
> +		list_for_each_prev(pos, group_list) {
> +			struct egroup *old = list_entry(pos, struct egroup, nd);
> +
> +			if (hashmap__size(&eg->pctx.ids) <=
> +			    hashmap__size(&old->pctx.ids))
> +				break;
> +		}
> +		list_add(&eg->nd, pos);
> +	}
>  
>  	return 0;
>  }
> -- 
> 2.26.2.645.ge9eca65c58-goog
>