mononoke: use logical number of cpus in our runtime

Summary:
We are using older version of tokio which spawns as many threads as we have
physical cores instead of the number of logical cores. It was fixed in
tokio-rs/tokio#2269 but we can't use it yet because
we are waiting for another fix to be released -
rust-lang/futures-rs#2154.

For now let's hardcode it in mononoke

Reviewed By: krallin

Differential Revision: D23599140

fbshipit-source-id: 80685651a7a29ba8938d9aa59770f191f7c42b8b

eden/mononoke/cmdlib/Cargo.toml

@@ -42,6 +42,7 @@ lazy_static = "1.0"
 libc = "0.2"
 log = { version = "0.4.8", features = ["kv_unstable"] }
 maplit = "1.0"
+num_cpus = "1.11"
 serde = { version = "1.0", features = ["derive", "rc"] }
 slog = { version = "2.5", features = ["max_level_debug"] }
 slog-term = "2.4.2"

eden/mononoke/cmdlib/src/helpers.rs

@@ -162,6 +162,10 @@ pub fn create_runtime(
     builder.name_prefix(log_thread_name_prefix.unwrap_or("tk"));
     if let Some(core_threads) = core_threads {
         builder.core_threads(core_threads);
+    } else {
+        // TODO(stash) T75113443 remove when
+        // https://github.com/tokio-rs/tokio/issues/2269 is landed
+        builder.core_threads(num_cpus::get());
     }
     builder.build()
 }