cat: avoid pipe() if stdout is pipe

Author: oech3

src/uu/cat/src/splice.rs

@@ -24,32 +24,43 @@ pub(super) fn write_fast_using_splice<R: FdReadable, S: AsRawFd + AsFd>(
     write_fd: &S,
 ) -> CatResult<bool> {
     use nix::fcntl::{FcntlArg, fcntl};
-    let (pipe_rd, pipe_wr) = pipe()?;
-    // improve performance
-    let _ = fcntl(
-        write_fd,
-        FcntlArg::F_SETPIPE_SZ(MAX_ROOTLESS_PIPE_SIZE as i32),
-    );
-
-    loop {
-        match splice(&handle.reader, &pipe_wr, MAX_ROOTLESS_PIPE_SIZE) {
-            Ok(n) => {
-                if n == 0 {
-                    return Ok(false);
+    const FIRST_PIPE_SIZE: usize = 64 * 1024;
+    if splice(&handle.reader, &write_fd, FIRST_PIPE_SIZE).is_ok() {
+        // fcntl improves performance for large file which is large overhead for small files
+        let _ = fcntl(
+            write_fd,
+            FcntlArg::F_SETPIPE_SZ(MAX_ROOTLESS_PIPE_SIZE as i32),
+        );
+        loop {
+            match splice(&handle.reader, &write_fd, MAX_ROOTLESS_PIPE_SIZE) {
+                Ok(1..) => {}
+                Ok(0) => return Ok(false),
+                Err(_) => return Ok(true),
+            }
+        }
+    } else {
+        // output is not pipe. Needs broker to use splice() which is high cost for small files
+        let (pipe_rd, pipe_wr) = pipe()?;
+        loop {
+            match splice(&handle.reader, &pipe_wr, MAX_ROOTLESS_PIPE_SIZE) {
+                Ok(n) => {
+                    if n == 0 {
+                        return Ok(false);
+                    }
+                    if splice_exact(&pipe_rd, write_fd, n).is_err() {
+                        // If the first splice manages to copy to the intermediate
+                        // pipe, but the second splice to stdout fails for some reason
+                        // we can recover by copying the data that we have from the
+                        // intermediate pipe to stdout using normal read/write. Then
+                        // we tell the caller to fall back.
+                        copy_exact(&pipe_rd, write_fd, n)?;
+                        return Ok(true);
+                    }
                 }
-                if splice_exact(&pipe_rd, write_fd, n).is_err() {
-                    // If the first splice manages to copy to the intermediate
-                    // pipe, but the second splice to stdout fails for some reason
-                    // we can recover by copying the data that we have from the
-                    // intermediate pipe to stdout using normal read/write. Then
-                    // we tell the caller to fall back.
-                    copy_exact(&pipe_rd, write_fd, n)?;
+                Err(_) => {
                     return Ok(true);
                 }
             }
-            Err(_) => {
-                return Ok(true);
-            }
         }
     }
 }