Add minor performance bump to shredding (#5956)

core/benches/shredder.rs

@@ -0,0 +1,34 @@
+#![feature(test)]
+
+extern crate test;
+
+use solana_core::shred::{Shredder, RECOMMENDED_FEC_RATE};
+use solana_sdk::signature::{Keypair, KeypairUtil};
+use std::sync::Arc;
+use test::Bencher;
+
+#[bench]
+fn bench_shredder(bencher: &mut Bencher) {
+    let kp = Arc::new(Keypair::new());
+    // 1Mb
+    let data = vec![0u8; 1000 * 1000];
+    bencher.iter(|| {
+        let mut shredder = Shredder::new(1, 0, RECOMMENDED_FEC_RATE, &kp, 0).unwrap();
+        bincode::serialize_into(&mut shredder, &data).unwrap();
+    })
+}
+
+#[bench]
+fn bench_deshredder(bencher: &mut Bencher) {
+    let kp = Arc::new(Keypair::new());
+    // 10MB
+    let data = vec![0u8; 10000 * 1000];
+    let mut shredded = Shredder::new(1, 0, 0.0, &kp, 0).unwrap();
+    let _ = bincode::serialize_into(&mut shredded, &data);
+    shredded.finalize_data();
+    let (_, shreds): (Vec<_>, Vec<_>) = shredded.shred_tuples.into_iter().unzip();
+    bencher.iter(|| {
+        let raw = &mut Shredder::deshred(&shreds).unwrap();
+        assert_ne!(raw.len(), 0);
+    })
+}

core/src/shred.rs

@@ -648,9 +648,8 @@ impl Shredder {
 
     /// Finalize a data shred. Update the shred index for the next shred
     fn finalize_data_shred(&mut self) {
-        let mut data = vec![0; PACKET_DATA_SIZE];
-        let mut wr = io::Cursor::new(&mut data[..]);
-        bincode::serialize_into(&mut wr, &self.active_shred).expect("Failed to serialize shred");
+        let mut data = Vec::with_capacity(PACKET_DATA_SIZE);
+        bincode::serialize_into(&mut data, &self.active_shred).expect("Failed to serialize shred");
 
         self.active_offset = 0;
         self.index += 1;