bb-imager: Improve sd card flashing performance

- Decreses sd card flashing time by 57% (only tested on Linux).
- Still slower than bb-imager but not by much.

Signed-off-by: Ayush Singh <ayush@beagleboard.org>

Cargo.lock

@@ -2657,6 +2657,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "603222e049bf0da71529325ada5d02dc3871cbd3679cf905429f7f0de93da87b"
 dependencies = [
  "liblzma-sys",
+ "num_cpus",
 ]
 
 [[package]]

bb-imager/Cargo.toml

@@ -8,7 +8,7 @@ repository.workspace = true
 license.workspace = true
 
 [dependencies]
-liblzma = { version = "0.3.5", features = ["static"] }
+liblzma = { version = "0.3.5", features = ["static", "parallel"] }
 chrono = { version = "0.4.38", features = ["serde"] }
 const-hex = { version = "1.13.1", features = ["serde"] }
 crc32fast = "1.4.2"

bb-imager/src/common.rs

@@ -15,7 +15,7 @@ use crate::{
     util,
 };
 
-pub(crate) const BUF_SIZE: usize = 32 * 1024;
+pub(crate) const BUF_SIZE: usize = 128 * 1024;
 
 #[derive(Error, Debug)]
 pub enum Error {

bb-imager/src/flasher/sd.rs

@@ -26,23 +26,17 @@ fn read_aligned(img: &mut crate::img::OsImage, buf: &mut [u8]) -> Result<usize>
         let count = img.read(&mut buf[pos..])?;
 
         if count == 0 {
-            break;
+            let end = pos + pos % 512;
+            buf[pos..end].fill(0);
+            return Ok(end);
         }
 
         pos += count;
-
+        // The buffer size is always a multiple of 512
         if pos % 512 == 0 {
-            break;
+            return Ok(pos);
         }
     }
-
-    if pos == 0 || pos % 512 == 0 {
-        Ok(pos)
-    } else {
-        let rem = pos % 512;
-        buf[pos..rem].fill(0);
-        Ok(pos + rem)
-    }
 }
 
 pub(crate) async fn flash<W>(
@@ -67,14 +61,14 @@ where
             break;
         }
 
+        tracing::debug!("Write: {} bytes", count);
+
+        sd.write_all(&buf[..count]).await?;
+
         pos += count;
         let _ = chan.try_send(DownloadFlashingStatus::FlashingProgress(
             pos as f32 / size as f32,
         ));
-
-        tracing::debug!("Write: {} bytes", count);
-
-        sd.write_all(&buf[..count]).await?;
     }
 
     if verify {

bb-imager/src/img.rs

@@ -63,7 +63,7 @@ impl OsImage {
                 let size = liblzma::uncompressed_size(&mut file)?;
 
                 file.seek(std::io::SeekFrom::Start(0))?;
-                let img = liblzma::read::XzDecoder::new(file);
+                let img = liblzma::read::XzDecoder::new_parallel(file);
                 let hasher = Sha256::new();
 
                 Ok(Self {

bb-imager/src/util.rs

@@ -26,16 +26,16 @@ pub(crate) async fn sha256_reader_progress<R: tokio::io::AsyncReadExt + Unpin>(
 
     loop {
         let count = reader.read(&mut buffer).await?;
-        pos += count;
-
-        let _ = chan.try_send(crate::DownloadFlashingStatus::VerifyingProgress(
-            pos as f32 / size as f32,
-        ));
 
         if count == 0 {
             break;
         }
         hasher.update(&buffer[..count]);
+
+        pos += count;
+        let _ = chan.try_send(crate::DownloadFlashingStatus::VerifyingProgress(
+            pos as f32 / size as f32,
+        ));
     }
 
     let hash = hasher