example: improve chunking speed example

by dropping the print-per-chunk and making the input buffer size configurable
(8k is the default when using `new()`).

this allows benchmarking various input buffer sizes. basically the same code is
used for image-based backups in proxmox-backup-client, but just the
reading and chunking part. looking at the flame graphs the smaller input
buffer sizes clearly show most of time spent polling, instead of
reading+copying (or reading and scanning and copying).

for a fixed chunk size stream with a 16G input file on tmpfs:

fixed 1M ran
    1.06 ± 0.17 times faster than fixed 4M
    1.22 ± 0.11 times faster than fixed 16M
    1.25 ± 0.09 times faster than fixed 512k
    1.31 ± 0.10 times faster than fixed 256k
    1.55 ± 0.13 times faster than fixed 128k
    1.92 ± 0.15 times faster than fixed 64k
    3.09 ± 0.31 times faster than fixed 32k
    4.76 ± 0.32 times faster than fixed 16k
    8.08 ± 0.59 times faster than fixed 8k

(from 15.275s down to 1.890s)

dynamic chunk stream, same input:

dynamic 4M ran
    1.01 ± 0.03 times faster than dynamic 1M
    1.03 ± 0.03 times faster than dynamic 16M
    1.06 ± 0.04 times faster than dynamic 512k
    1.07 ± 0.03 times faster than dynamic 128k
    1.12 ± 0.03 times faster than dynamic 64k
    1.15 ± 0.20 times faster than dynamic 256k
    1.23 ± 0.03 times faster than dynamic 32k
    1.47 ± 0.04 times faster than dynamic 16k
    1.92 ± 0.05 times faster than dynamic 8k

(from 26.5s down to 13.772s)

same input file on ext4 on LVM on CT2000P5PSSD8 (with caches dropped for each run):

fixed 4M ran
   1.06 ± 0.02 times faster than fixed 16M
   1.10 ± 0.01 times faster than fixed 1M
   1.12 ± 0.01 times faster than fixed 512k
   1.15 ± 0.02 times faster than fixed 128k
   1.17 ± 0.01 times faster than fixed 256k
   1.22 ± 0.02 times faster than fixed 64k
   1.55 ± 0.05 times faster than fixed 32k
   2.00 ± 0.07 times faster than fixed 16k
   3.01 ± 0.15 times faster than fixed 8k

(from 19.807s down to 6.574s)

dynamic 4M ran
    1.04 ± 0.02 times faster than dynamic 512k
    1.04 ± 0.02 times faster than dynamic 128k
    1.04 ± 0.02 times faster than dynamic 16M
    1.06 ± 0.02 times faster than dynamic 1M
    1.06 ± 0.02 times faster than dynamic 256k
    1.08 ± 0.02 times faster than dynamic 64k
    1.16 ± 0.02 times faster than dynamic 32k
    1.34 ± 0.03 times faster than dynamic 16k
    1.70 ± 0.04 times faster than dynamic 8k

(from 31.184s down to 18.378s)

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>

examples/test_chunk_speed2.rs

@@ -1,9 +1,12 @@
+use std::str::FromStr;
+
 use anyhow::Error;
 use futures::*;
 
 extern crate proxmox_backup;
 
-use pbs_client::ChunkStream;
+use pbs_client::{ChunkStream, FixedChunkStream};
+use proxmox_human_byte::HumanByte;
 
 // Test Chunker with real data read from a file.
 //
@@ -21,9 +24,19 @@ fn main() {
 async fn run() -> Result<(), Error> {
     let file = tokio::fs::File::open("random-test.dat").await?;
 
-    let stream = tokio_util::codec::FramedRead::new(file, tokio_util::codec::BytesCodec::new())
-        .map_ok(|bytes| bytes.to_vec())
-        .map_err(Error::from);
+    let mut args = std::env::args();
+    args.next();
+
+    let buffer_size = args.next().unwrap_or("8k".to_string());
+    let buffer_size = HumanByte::from_str(&buffer_size)?;
+    println!("Using buffer size {buffer_size}");
+
+    let stream = tokio_util::codec::FramedRead::with_capacity(
+        file,
+        tokio_util::codec::BytesCodec::new(),
+        buffer_size.as_u64() as usize,
+    )
+    .map_err(Error::from);
 
     //let chunk_stream = FixedChunkStream::new(stream, 4*1024*1024);
     let mut chunk_stream = ChunkStream::new(stream, None, None, None);
@@ -40,7 +53,7 @@ async fn run() -> Result<(), Error> {
         repeat += 1;
         stream_len += chunk.len();
 
-        println!("Got chunk {}", chunk.len());
+        //println!("Got chunk {}", chunk.len());
     }
 
     let speed =