cat, tail, head:allways splice with broker pipe for throughput

src/uucore/src/lib/features/pipes.rs

@@ -82,24 +82,22 @@ pub fn might_fuse(source: &impl AsFd) -> bool {
     rustix::fs::fstatfs(source).map_or(true, |stats| stats.f_type == 0x6573_5546) // FUSE magic number, too many platform specific clippy warning with const
 }
 
-/// splice all of source to dest
-/// returns Ok(()) at end of file
-#[inline]
-fn splice_unbounded(source: &impl AsFd, dest: &mut impl AsFd) -> rustix::io::Result<()> {
-    while splice(&source, &dest, MAX_ROOTLESS_PIPE_SIZE)? > 0 {}
-    Ok(())
-}
-
 /// force-splice source to dest even both of them are not pipe via broker pipe
 ///
-/// This should not be used if one of them are pipe to save resources
+/// throughput is better than direct splice for the case one of in/output is pipe by unknown reason
+/// This includes read ahead and optimization for stdout's pipe size
 #[inline]
-fn splice_unbounded_broker(source: &impl AsFd, dest: &mut impl AsFd) -> PipeRes {
+pub fn splice_unbounded_auto(source: &impl AsFd, dest: &mut impl AsFd) -> PipeRes {
     static PIPE_CACHE: OnceLock<Option<(PipeReader, PipeWriter)>> = OnceLock::new();
     let Some((pipe_rd, pipe_wr)) = PIPE_CACHE.get_or_init(|| pipe::<false>().ok()) else {
         return Ok(Err(()));
     };
-
+    // fcntl for input would not improve throughput since
+    // - sender with splice probably increased size already
+    // - sender without splice is bottleneck
+    let _ = fcntl_setpipe_size(&mut *dest, MAX_ROOTLESS_PIPE_SIZE);
+    // pre-generate page caches for splice
+    let _ = rustix::fs::fadvise(source, 0, None, rustix::fs::Advice::Sequential);
     loop {
         match splice(&source, &pipe_wr, MAX_ROOTLESS_PIPE_SIZE) {
             Ok(0) => return Ok(Ok(())),
@@ -113,23 +111,6 @@ fn splice_unbounded_broker(source: &impl AsFd, dest: &mut impl AsFd) -> PipeRes
     }
 }
 
-/// try splice_unbounded 1st and splice_unbounded_broker if both of in/output are not pipe
-/// This includes read ahead and optimization for stdout's pipe size
-#[inline]
-pub fn splice_unbounded_auto(source: &impl AsFd, dest: &mut impl AsFd) -> PipeRes {
-    // fcntl for input would not improve throughput since
-    // - sender with splice probably increased size already
-    // - sender without splice is bottleneck
-    let is_pipe_out = fcntl_setpipe_size(&mut *dest, MAX_ROOTLESS_PIPE_SIZE).is_ok();
-    // pre-generate page caches for splice
-    let is_file_in = rustix::fs::fadvise(source, 0, None, rustix::fs::Advice::Sequential).is_ok();
-    if (is_file_in && !is_pipe_out) || splice_unbounded(source, dest).is_err() {
-        // both of in/output are not pipe
-        return splice_unbounded_broker(source, dest);
-    }
-    Ok(Ok(()))
-}
-
 /// splice `n` bytes with read/write fallback
 /// return actually sent bytes
 #[inline]
@@ -143,52 +124,37 @@ pub fn send_n_bytes(input: impl AsFd, target: impl AsFd, n: u64) -> std::io::Res
     }
     let mut n = n;
     let mut bytes_written: u64 = 0;
-    let succeed_or_fuse = loop {
-        if n == 0 {
-            // avoid unnecessary syscall
-            return Ok(bytes_written);
-        }
-        match splice(&input, &target, n as usize) {
-            Ok(0) => break true,
-            Ok(s) => {
-                n -= s as u64;
-                bytes_written += s as u64;
+    let succeed_or_fuse = if let Some((broker_r, broker_w)) = PIPE_CACHE
+        .get_or_init(|| {
+            // use std::io::pipe to avoid unnecessary fcntl
+            let pair = std::io::pipe().ok()?;
+            if pipe_size > KERNEL_DEFAULT_PIPE_SIZE {
+                let _ = fcntl_setpipe_size(&pair.0, pipe_size);
             }
-            _ => break false, // input or output is not pipe
-        }
-    };
-    let succeed_or_fuse = succeed_or_fuse
-        || if let Some((broker_r, broker_w)) = PIPE_CACHE
-            .get_or_init(|| {
-                // use std::io::pipe to avoid unnecessary fcntl
-                let pair = std::io::pipe().ok()?;
-                if pipe_size > KERNEL_DEFAULT_PIPE_SIZE {
-                    let _ = fcntl_setpipe_size(&pair.0, pipe_size);
-                }
-                Some(pair)
-            })
-            .as_ref()
-        {
-            // todo: create fn splice_bounded_broker
-            loop {
-                if n == 0 {
-                    return Ok(bytes_written);
-                }
-                match splice(&input, &broker_w, n as usize) {
-                    Ok(0) => break true,
-                    Ok(s) => {
-                        n -= s as u64;
-                        bytes_written += s as u64;
-                        if drain_pipe(broker_r, &target, s)?.is_err() {
-                            break false;
-                        }
+            Some(pair)
+        })
+        .as_ref()
+    {
+        // todo: create fn splice_bounded_broker
+        loop {
+            if n == 0 {
+                return Ok(bytes_written);
+            }
+            match splice(&input, &broker_w, n as usize) {
+                Ok(0) => break true,
+                Ok(s) => {
+                    n -= s as u64;
+                    bytes_written += s as u64;
+                    if drain_pipe(broker_r, &target, s)?.is_err() {
+                        break false;
                     }
-                    _ => break false,
                 }
+                _ => break false,
             }
-        } else {
-            false
-        };
+        }
+    } else {
+        false
+    };
     // do not always fallback to write for fuse, or 2 Ctrl+D is required to exit on tty
     // todo: move fuse patch to callers
     if !succeed_or_fuse || might_fuse(&input) {