Module Name: src
Committed By: ad
Date: Wed Oct 4 22:12:23 UTC 2023
Modified Files:
src/sys/kern: sys_pipe.c
Log Message:
pipe_read(): try to skip locking the pipe if a non-blocking fd is used, as
is very often the case with BSD make (from FreeBSD/mjg@).
To generate a diff of this commit:
cvs rdiff -u -r1.160 -r1.161 src/sys/kern/sys_pipe.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/sys_pipe.c
diff -u src/sys/kern/sys_pipe.c:1.160 src/sys/kern/sys_pipe.c:1.161
--- src/sys/kern/sys_pipe.c:1.160 Sat Apr 22 13:53:02 2023
+++ src/sys/kern/sys_pipe.c Wed Oct 4 22:12:23 2023
@@ -1,4 +1,4 @@
-/* $NetBSD: sys_pipe.c,v 1.160 2023/04/22 13:53:02 riastradh Exp $ */
+/* $NetBSD: sys_pipe.c,v 1.161 2023/10/04 22:12:23 ad Exp $ */
/*-
* Copyright (c) 2003, 2007, 2008, 2009 The NetBSD Foundation, Inc.
@@ -68,7 +68,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: sys_pipe.c,v 1.160 2023/04/22 13:53:02 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: sys_pipe.c,v 1.161 2023/10/04 22:12:23 ad Exp $");
#include <sys/param.h>
#include <sys/systm.h>
@@ -434,6 +434,23 @@ pipe_read(file_t *fp, off_t *offset, str
size_t ocnt;
unsigned int wakeup_state = 0;
+ /*
+ * Try to avoid locking the pipe if we have nothing to do.
+ *
+ * There are programs which share one pipe amongst multiple processes
+ * and perform non-blocking reads in parallel, even if the pipe is
+ * empty. This in particular is the case with BSD make, which when
+ * spawned with a high -j number can find itself with over half of the
+ * calls failing to find anything.
+ */
+ if ((fp->f_flag & FNONBLOCK) != 0) {
+ if (__predict_false(uio->uio_resid == 0))
+ return (0);
+ if (atomic_load_relaxed(&bp->cnt) == 0 &&
+ (atomic_load_relaxed(&rpipe->pipe_state) & PIPE_EOF) == 0)
+ return (EAGAIN);
+ }
+
mutex_enter(lock);
++rpipe->pipe_busy;
ocnt = bp->cnt;
