Re: Linux 2.6.29

Janne Grunau
2009-04-04T16:30:32Z

On Fri, Apr 03, 2009 at 07:30:37PM -0400, Jeff Garzik wrote:
> David Rees wrote:
> > The *only* reason MythTV fsyncs (or fdatasyncs) the data to disk all
> > the time is to keep a large amount of dirty pages from building up and
> > then causing horrible latencies when that data starts getting flushed
> > to disk.
>
> sync_file_range() will definitely help that situation.

Jeff, could you please try following patch for 0.21 or update to the
latest trunk revision. I don't have a way to reproduce the high
latencies with fdatasync on ext3, data=ordered. Doing a parallel
"dd if=/dev/zero of=file" on the same partition introduces even with
sync_file_range latencies over 1 second.

Janne

---

Index: configure
===================================================================
--- configure (revision 20302)
+++ configure (working copy)
@@ -873,6 +873,7 @@
sdl_video_size
soundcard_h
stdint_h
+ sync_file_range
sys_poll_h
sys_soundcard_h
termios_h
@@ -2413,6 +2414,17 @@
int main( void ) { return (round(3.999f) > 0)?0:1; }
EOF

+# test for sync_file_range (linux only system call since 2.6.17)
+check_ld <<EOF && enable sync_file_range
+#define _GNU_SOURCE
+#include <fcntl.h>
+
+int main(int argc, char **argv){
+ sync_file_range(0,0,0,0);
+ return 0;
+}
+EOF
+
# test for sizeof(int)
for sizeof in 1 2 4 8 16; do
check_cc <<EOF && _sizeof_int=$sizeof && break
Index: libs/libmythtv/ThreadedFileWriter.cpp
===================================================================
--- libs/libmythtv/ThreadedFileWriter.cpp (revision 20302)
+++ libs/libmythtv/ThreadedFileWriter.cpp (working copy)
@@ -18,6 +18,7 @@
#include "ThreadedFileWriter.h"
#include "mythcontext.h"
#include "compat.h"
+#include "mythconfig.h"

#if defined(_POSIX_SYNCHRONIZED_IO) && _POSIX_SYNCHRONIZED_IO > 0
#define HAVE_FDATASYNC
@@ -122,6 +123,7 @@
// file stuff
filename(QDeepCopy<QString>(fname)), flags(pflags),
mode(pmode), fd(-1),
+ m_file_sync(0), m_file_wpos(0),
// state
no_writes(false), flush(false),
in_dtor(false), ignore_writes(false),
@@ -154,6 +156,8 @@
buf = new char[TFW_DEF_BUF_SIZE + 1024];
bzero(buf, TFW_DEF_BUF_SIZE + 64);

+ m_file_sync = m_file_wpos = 0;
+
tfw_buf_size = TFW_DEF_BUF_SIZE;
tfw_min_write_size = TFW_MIN_WRITE_SIZE;
pthread_create(&writer, NULL, boot_writer, this);
@@ -292,7 +296,22 @@
{
if (fd >= 0)
{
-#ifdef HAVE_FDATASYNC
+#ifdef HAVE_SYNC_FILE_RANGE
+ uint64_t write_position;
+
+ buflock.lock();
+ write_position = m_file_wpos;
+ buflock.unlock();
+
+ if ((write_position - m_file_sync) > TFW_MAX_WRITE_SIZE ||
+ (write_position && m_file_sync < (uint64_t)tfw_min_write_size))
+ {
+ sync_file_range(fd, m_file_sync, write_position - m_file_sync,
+ SYNC_FILE_RANGE_WRITE);
+ m_file_sync = write_position;
+ }
+
+#elif defined(HAVE_FDATASYNC)
fdatasync(fd);
#else
fsync(fd);
@@ -414,6 +433,7 @@

buflock.lock();
rpos = (rpos + size) % tfw_buf_size;
+ m_file_wpos += size;
buflock.unlock();

bufferWroteData.wakeAll();
Index: libs/libmythtv/ThreadedFileWriter.h
===================================================================
--- libs/libmythtv/ThreadedFileWriter.h (revision 20302)
+++ libs/libmythtv/ThreadedFileWriter.h (working copy)
@@ -40,6 +40,8 @@
int flags;
mode_t mode;
int fd;
+ uint64_t m_file_sync; ///< offset synced to disk
+ uint64_t m_file_wpos; ///< offset written to disk

// state
bool no_writes;