Added basic benchmarking [skip ci]

Rakefile

@@ -7,3 +7,55 @@ Rake::TestTask.new do |t|
   t.pattern = "test/**/*_test.rb"
   t.warning = false # for daru
 end
+
+# TODO use benchmark-ips
+def benchmark_user_recs(name, recommender)
+  ms = Benchmark.realtime do
+    recommender.user_ids.each do |user_id|
+      recommender.user_recs(user_id)
+    end
+  end
+  puts "%-8s %f" % [name, ms]
+end
+
+# TODO use benchmark-ips
+def benchmark_item_recs(name, recommender)
+  ms = Benchmark.realtime do
+    recommender.item_ids.each do |item_id|
+      recommender.item_recs(item_id)
+    end
+  end
+  puts "%-8s %f" % [name, ms]
+end
+
+namespace :benchmark do
+  task :user_recs do
+    require "bundler/setup"
+    Bundler.require
+    require "benchmark"
+
+    data = Disco.load_movielens
+    recommender = Disco::Recommender.new
+    recommender.fit(data)
+
+    benchmark_user_recs("none", recommender)
+    recommender.optimize_user_recs
+    benchmark_user_recs("faiss", recommender)
+  end
+
+  task :item_recs do
+    require "bundler/setup"
+    Bundler.require
+    require "benchmark"
+
+    data = Disco.load_movielens
+    recommender = Disco::Recommender.new
+    recommender.fit(data)
+
+    benchmark_item_recs("none", recommender)
+    recommender.optimize_item_recs(library: "ngt")
+    benchmark_item_recs("ngt", recommender)
+    recommender.optimize_item_recs(library: "faiss")
+    benchmark_item_recs("faiss", recommender)
+  end
+end