From: Anton Ivanov <antiv...@cisco.com>
If the ubd is asynchronous the amount of time uml will spend
fsync-ing on FLUSH is unpredictable. There are bits in the upper fs
layers that really dislike this. Replacing fsync() with an
async flush request via sync_file_range mitigates this (somewhat),
improves performance significantly without making filesystem integrity
much worse (compared to the original async writes + flush).
Signed-off-by: Anton Ivanov <antiv...@cisco.com>
---
arch/um/drivers/ubd.h | 1 +
arch/um/drivers/ubd_kern.c | 2 +-
arch/um/drivers/ubd_user.c | 7 +++++++
3 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/arch/um/drivers/ubd.h b/arch/um/drivers/ubd.h
index 3b48cd2..5847fff 100644
--- a/arch/um/drivers/ubd.h
+++ b/arch/um/drivers/ubd.h
@@ -8,6 +8,7 @@
#define __UM_UBD_USER_H
extern int start_io_thread(unsigned long sp, int *fds_out);
+extern int ubd_async_fsync(int fd);
extern int io_thread(void *arg);
extern int kernel_fd;
diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 80f8655..ccfaa9d 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -1410,7 +1410,7 @@ static void do_io(struct io_thread_req *req)
if (req->op == UBD_FLUSH) {
/* fds[0] is always either the rw image or our cow file */
- n = os_sync_file(req->fds[0]);
+ n = ubd_async_fsync(req->fds[0]);
if (n != 0) {
printk("do_io - sync failed err = %d "
"fd = %d\n", -n, req->fds[0]);
diff --git a/arch/um/drivers/ubd_user.c b/arch/um/drivers/ubd_user.c
index 6833fc5..4970087 100644
--- a/arch/um/drivers/ubd_user.c
+++ b/arch/um/drivers/ubd_user.c
@@ -17,10 +17,17 @@
#include <sys/param.h>
#include <endian.h>
#include <byteswap.h>
+#include <fcntl.h>
#include "ubd.h"
#include <os.h>
+int ubd_async_fsync(int fd) {
+ int ret;
+ CATCH_EINTR(ret = sync_file_range(fd, 0, 0, SYNC_FILE_RANGE_WRITE));
+ return ret;
+}
+
int start_io_thread(unsigned long sp, int *fd_out)
{
int pid, fds[2], err;
--
1.7.10.4
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