[Backport] Don't explcitly include virtual device in hash (#6167)

test/test_persistent_cache.py

@@ -69,6 +69,18 @@ def _spmd_replicated_test(tmpdir, metrics):
   _assert_correctness_and_metrics(t, xt, metrics)
 
 
+def _spmd_explicitly_replicated_test(tmpdir, metrics):
+  xr.initialize_cache(tmpdir)
+  xr.use_spmd()
+  t = torch.randn(16)
+  xt = t.to(xm.xla_device())
+
+  n_dev = xr.global_runtime_device_count()
+  mesh = xs.Mesh(range(n_dev), (n_dev,))
+  xs.mark_sharding(xt, mesh, (None,))
+  _assert_correctness_and_metrics(t, xt, metrics)
+
+
 def _spmd_sharded_test(tmpdir, metrics):
   xr.initialize_cache(tmpdir)
   xr.use_spmd()
@@ -124,6 +136,20 @@ def test_persistent_cache_mp(self):
   def test_persistent_cache(self, test_fn):
     self._run_test(_test_spawn, test_fn)
 
+  @absltest.skipUnless(xr.device_type() == 'TPU', 'TPU required for SPMD')
+  @run_with_tmpdir
+  def test_replicated_spmd_hash(self, tmpdir):
+    # The hash should differ between replicated SPMD and the single-device test.
+    _test_spawn(_spmd_explicitly_replicated_test, (tmpdir, {
+        'PersistentCacheMiss': 1,
+        'PersistentCacheHit': None
+    }))
+
+    _test_spawn(_single_device_test, (tmpdir, {
+        'PersistentCacheMiss': 1,
+        'PersistentCacheHit': None
+    }))
+
 
 if __name__ == '__main__':
   test = absltest.main()

torch_xla/csrc/runtime/pjrt_computation_client.cc

@@ -89,8 +89,6 @@ torch::lazy::hash_t hash_comp_env(
     std::shared_ptr<xla::PjRtClient> client,
     std::vector<xla::PjRtDevice*>& ordered_devices) {
   torch::lazy::hash_t hash = hash::HashXlaEnvVars();
-  // Whether or not SPMD mode is active should influence the hash.
-  hash = torch::lazy::HashCombine(hash, UseVirtualDevice());
   auto topology_desc = client->GetTopologyDescription();
   if (topology_desc.ok()) {
     // Some backends support a topology description which provides a better
@@ -244,6 +242,7 @@ PjRtComputationClient::PjRtComputationClient() {
     std::string device_str = PjRtDeviceToString(device);
     string_to_device_.emplace(device_str, device);
   }
+  comp_env_hash_ = hash_comp_env(client_, ordered_devices);
 
   auto tracked_devices = GetLocalDevices();
   tracked_devices.emplace_back(spmd_device_str);