Algorithm takes 5sec but the page takes 1.5m to load

After calling a process via ajax

if ($('#content-recommendation').length) {
    $.ajax({
    url:'/get_content_recommendation/' + gon.item_id + '.js',
    type:"get"
  });
}

I do the following in itens_controller/get_content_recommendation

before_action :set_item, only: [:get_content_recommendation,...]
...
def get_content_recommendation
  # GET /itens/1

  start_t = Time.now

  @itens_recomendados_conteudo = @item.get_tf_idf_recommendations

  finish_t = Time.now
  puts "Tempo para realizar todo o processo: " + (finish_t - start_t).to_s + "segundos"

  respond_to do |format|
    format.js
  end

end

In item#get_tf_idf_recommendations

def get_tf_idf_recommendations

# Esse cara está com problema!

  Item.all.includes(:generos).each do |item|
    aux = Array.new 
    item.generos.each do |gen| 
      aux << gen.id
    end
  data << aux
  end
# -----

# Codigo deveria continuar mas o retorno é apenas para mostrar os itens na view quando o ajax é carregado
return Item.first
end

My code to change the html is in views/item#get_content_recommendation.js.erb

$("#content-recommendation").html("<%= 'Apareceu!' %>")

The code for item#get_tf_idf_recommendations marked as problematic is for some reason delaying the response of my ajax the time marked after execution by start_t - finish_t is Tempo para realizar todo o processo: 4.923116s but ajax only appears after 1m: 30s . If I comment on the code with problem the text appears in time.

In the log there is nothing abnormal:

Started GET "/get_content_recommendation/1.js" for 127.0.0.1 at 2014-08-23 11:29:34 -0300
Processing by ItensController#get_content_recommendation as JS
  Parameters: {"id"=>"1"}
  Item Load (0.4ms)  SELECT  'itens'.* FROM 'itens'  WHERE 'itens'.'id' = 1 LIMIT 1
  Item Load (9.2ms)  SELECT 'itens'.* FROM 'itens'
  Generalizacao Load (13.4ms)  SELECT 'generalizacoes'.* FROM 'generalizacoes'  WHERE 'generalizacoes'.'item_id' IN (1, 2, ... 1749, 1750, 1751, 1752)

  Genero Load (0.6ms)  SELECT 'generos'.* FROM 'generos'  WHERE 'generos'.'id' IN (1, 12, ... 30, 29)

  Item Load (0.5ms)  SELECT  'itens'.* FROM 'itens'  LIMIT 5
Tempo para realizar todo o processo: 4.923116segundos
    Rendered itens/_content_recommendation.html.erb (0.8ms)
    Rendered itens/get_content_recommendation.js.erb (2.2ms)
Completed 200 OK in 4932ms (Views: 5.5ms | ActiveRecord: 24.2ms | Solr: 0.0ms)

EDIT:

After removing ajax and loading in a normal full request, I saw that the problem is not ajax, but it's performance problem in the algorithm ... The time is still the same 5.03214s after the log is:

...
Rendered itens/_avaliacoes.html.erb (3.7ms)
Rendered itens/_content_recommendation.html.erb (1.3ms)
Rendered itens/show.html.erb within layouts/application (693.6ms)
Rendered layouts/_header.html.erb (5.1ms)
Rendered layouts/_footer.html.erb (0.4ms)
Completed 200 OK in 6396ms (Views: 1194.7ms | ActiveRecord: 61.7ms | Solr: 0.0ms)

But the page only loads after 1.5m as seen by the Google Chrome trace:

Blocking    0.987 ms
DNS Lookup  624.962 ms
Connecting  0.412 ms
Sending 0.129 ms
Waiting 1.5 min
Receiving 1.441 ms

The worst thing is that it does not stop to know what is taking and how to improve!