Disable rugged auto-detect when Puma threads>1

If Puma is in use and Puma threads is more than 1, it is expected to
have performance lose by using Rugged patches, because of Rugged calls
does not release Ruby GVL while doing IO. So in this case, we will
ignore rugged automatic detect `can_use_disk?`.

lib/gitlab/git/rugged_impl/use_rugged.rb

@@ -8,9 +8,17 @@ module Gitlab
           feature = Feature.get(feature_key)
           return feature.enabled? if Feature.persisted?(feature)
 
+          # Disable Rugged auto-detect(can_use_disk?) when Puma threads>1
+          # https://gitlab.com/gitlab-org/gitlab/issues/119326
+          return false if running_puma_with_multiple_threads?
+
           Gitlab::GitalyClient.can_use_disk?(repo.storage)
         end
 
+        def running_puma_with_multiple_threads?
+          Gitlab::Runtime.puma? && ::Puma.cli_config.options[:max_threads] > 1
+        end
+
         def execute_rugged_call(method_name, *args)
           Gitlab::GitalyClient::StorageSettings.allow_disk_access do
             start = Gitlab::Metrics::System.monotonic_time

spec/lib/gitlab/git/rugged_impl/use_rugged_spec.rb

@@ -53,6 +53,21 @@ describe Gitlab::Git::RuggedImpl::UseRugged, :seed_helper do
       allow(Feature).to receive(:persisted?).with(feature_flag).and_return(false)
     end
 
+    context 'when running puma with multiple threads' do
+      before do
+        allow(subject).to receive(:running_puma_with_multiple_threads?).and_return(true)
+      end
+
+      it 'returns false' do
+        expect(subject.use_rugged?(repository, feature_flag_name)).to be false
+      end
+    end
+
+    context 'when not running puma with multiple threads' do
+      before do
+        allow(subject).to receive(:running_puma_with_multiple_threads?).and_return(false)
+      end
+
       it 'returns true when gitaly matches disk' do
         expect(subject.use_rugged?(repository, feature_flag_name)).to be true
       end
@@ -79,6 +94,7 @@ describe Gitlab::Git::RuggedImpl::UseRugged, :seed_helper do
         subject.use_rugged?(repository, feature_flag_name)
       end
     end
+  end
 
   context 'when feature flag is persisted' do
     before do
@@ -99,6 +115,37 @@ describe Gitlab::Git::RuggedImpl::UseRugged, :seed_helper do
     end
   end
 
+  describe '#running_puma_with_multiple_threads?' do
+    context 'when using Puma' do
+      before do
+        stub_const('::Puma', class_double('Puma'))
+        allow(Gitlab::Runtime).to receive(:puma?).and_return(true)
+      end
+
+      it 'returns false for single thread Puma' do
+        allow(::Puma).to receive_message_chain(:cli_config, :options).and_return(max_threads: 1)
+
+        expect(subject.running_puma_with_multiple_threads?).to be false
+      end
+
+      it 'returns true for multi-threaded Puma' do
+        allow(::Puma).to receive_message_chain(:cli_config, :options).and_return(max_threads: 2)
+
+        expect(subject.running_puma_with_multiple_threads?).to be true
+      end
+    end
+
+    context 'when not using Puma' do
+      before do
+        allow(Gitlab::Runtime).to receive(:puma?).and_return(false)
+      end
+
+      it 'returns false' do
+        expect(subject.running_puma_with_multiple_threads?).to be false
+      end
+    end
+  end
+
   def create_temporary_gitaly_metadata_file
     tmp = Tempfile.new('.gitaly-metadata')
     gitaly_metadata = {