diff --git a/src/libcore/benches/fmt.rs b/src/libcore/benches/fmt.rs
new file mode 100644
index 00000000000..92f10c760c6
--- /dev/null
+++ b/src/libcore/benches/fmt.rs
@@ -0,0 +1,110 @@
+use std::io::{self, Write as IoWrite};
+use std::fmt::{self, Write as FmtWrite};
+use test::Bencher;
+
+#[bench]
+fn write_vec_value(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = Vec::new();
+        for _ in 0..1000 {
+            mem.write_all("abc".as_bytes()).unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_vec_ref(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = Vec::new();
+        let wr = &mut mem as &mut dyn io::Write;
+        for _ in 0..1000 {
+            wr.write_all("abc".as_bytes()).unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_vec_macro1(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = Vec::new();
+        let wr = &mut mem as &mut dyn io::Write;
+        for _ in 0..1000 {
+            write!(wr, "abc").unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_vec_macro2(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = Vec::new();
+        let wr = &mut mem as &mut dyn io::Write;
+        for _ in 0..1000 {
+            write!(wr, "{}", "abc").unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_vec_macro_debug(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = Vec::new();
+        let wr = &mut mem as &mut dyn io::Write;
+        for _ in 0..1000 {
+            write!(wr, "{:?}", "☃").unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_str_value(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = String::new();
+        for _ in 0..1000 {
+            mem.write_str("abc").unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_str_ref(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = String::new();
+        let wr = &mut mem as &mut dyn fmt::Write;
+        for _ in 0..1000 {
+            wr.write_str("abc").unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_str_macro1(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = String::new();
+        for _ in 0..1000 {
+            write!(mem, "abc").unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_str_macro2(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = String::new();
+        let wr = &mut mem as &mut dyn fmt::Write;
+        for _ in 0..1000 {
+            write!(wr, "{}", "abc").unwrap();
+        }
+    });
+}
+
+#[bench]
+fn write_str_macro_debug(bh: &mut Bencher) {
+    bh.iter(|| {
+        let mut mem = String::new();
+        let wr = &mut mem as &mut dyn fmt::Write;
+        for _ in 0..1000 {
+            write!(wr, "{:?}", "☃").unwrap();
+        }
+    });
+}
diff --git a/src/libcore/benches/lib.rs b/src/libcore/benches/lib.rs
index 5b4971c81dd..48572af611a 100644
--- a/src/libcore/benches/lib.rs
+++ b/src/libcore/benches/lib.rs
@@ -11,3 +11,4 @@ mod iter;
 mod num;
 mod ops;
 mod slice;
+mod fmt;