Linux 2.6.35+ allows pipe buffer resizing via fcntl(2). When
running multi-threaded SoX invocations with large buffers, the
default pipe size (64K) can be too small and become a bottleneck
for IPC. Increasing the pipe to the maximum allowed size
reduces the amount of stalls in data flow between processes (SoX
or otherwise).
When using SOX_OPTS="--multi-thread --buffer 131072" on a 4-core
system, a command like:
sox -M "|sox $< -p $(lft_fx)" "|sox $< -p $(rgt_fx)" $@
..can run significantly faster (10-80%) depending on the
processing chain, file sizes/formats and effects in use.
Before this patch, using "--buffer 131072" could be hugely
detrimental to performance due to the pipe being only half
the size (64K) of the SoX buffer.
---
src/formats.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 51 insertions(+)
diff --git a/src/formats.c b/src/formats.c
index f3efe764..1da8489c 100644
--- a/src/formats.c
+++ b/src/formats.c
@@ -18,6 +18,7 @@
* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
+#define _GNU_SOURCE
#include "sox_i.h"
#include <assert.h>
@@ -37,6 +38,10 @@
#include <magic.h>
#endif
+#ifdef HAVE_UNISTD_H
+# include <unistd.h>
+#endif
+
#define PIPE_AUTO_DETECT_SIZE 256 /* Only as much as we can rewind a pipe */
#define AUTO_DETECT_SIZE 4096 /* For seekable file, so no restriction */
@@ -370,6 +375,50 @@ static int xfclose(FILE * file, lsx_io_type io_type)
fclose(file);
}
+static void incr_pipe_size(FILE *f)
+{
+/*
+ * Linux 2.6.35 and later has the ability to expand the pipe buffer
+ * Try to get it as big as possible to avoid stalls when SoX itself
+ * is using big buffers
+ */
+#if defined(F_GETPIPE_SZ) && defined(F_SETPIPE_SZ)
+ static long max_pipe_size;
+
+ /* read the maximum size of the pipe the first time this is called */
+ if (max_pipe_size == 0) {
+ const char path[] = "/proc/sys/fs/pipe-max-size";
+ int fd = open(path, O_RDONLY);
+
+ max_pipe_size = -1;
+ if (fd >= 0) {
+ char buf[80];
+ ssize_t r = read(fd, buf, sizeof(buf));
+
+ if (r > 0) {
+ buf[r] = 0;
+ max_pipe_size = strtol(buf, NULL, 10);
+
+ /* guard against obviously wrong values on messed up systems */
+ if (max_pipe_size <= PIPE_BUF || max_pipe_size > INT_MAX)
+ max_pipe_size = -1;
+ }
+ close(fd);
+ }
+ }
+
+ if (max_pipe_size > PIPE_BUF) {
+ int fd = fileno(f);
+
+ if (fcntl(fd, F_SETPIPE_SZ, max_pipe_size) >= 0)
+ lsx_debug("got pipe %ld bytes\n", max_pipe_size);
+ else
+ lsx_warn("couldn't set pipe size to %ld bytes: %s\n",
+ max_pipe_size, strerror(errno));
+ }
+#endif /* do nothing for platforms without F_{GET,SET}PIPE_SZ */
+}
+
static FILE * xfopen(char const * identifier, char const * mode, lsx_io_type *
io_type)
{
*io_type = lsx_io_file;
@@ -382,6 +431,7 @@ static FILE * xfopen(char const * identifier, char const *
mode, lsx_io_type * i
#endif
f = popen(identifier + 1, POPEN_MODE);
*io_type = lsx_io_pipe;
+ incr_pipe_size(f);
#else
lsx_fail("this build of SoX cannot open pipes");
#endif
@@ -394,6 +444,7 @@ static FILE * xfopen(char const * identifier, char const *
mode, lsx_io_type * i
char * command = lsx_malloc(strlen(command_format) + strlen(identifier));
sprintf(command, command_format, identifier);
f = popen(command, POPEN_MODE);
+ incr_pipe_size(f);
free(command);
*io_type = lsx_io_url;
#else
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