I am going to send in a couple of more which bulk-up the transactions
(this forms most of the improvement) later this week.
This one is obvious - qemu has been using it for ages.
A.
On 08/11/15 15:20, Anton Ivanov wrote:
> This decreases the number of syscalls per read/write by half.
>
> Signed-off-by: Anton Ivanov <aiva...@brocade.com>
> ---
> arch/um/drivers/ubd_kern.c | 27 +++++----------------------
> arch/um/include/shared/os.h | 2 ++
> arch/um/os-Linux/file.c | 19 +++++++++++++++++++
> 3 files changed, 26 insertions(+), 22 deletions(-)
>
> diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
> index e8ab93c..39ba207 100644
> --- a/arch/um/drivers/ubd_kern.c
> +++ b/arch/um/drivers/ubd_kern.c
> @@ -535,11 +535,7 @@ static int read_cow_bitmap(int fd, void *buf, int
> offset, int len)
> {
> int err;
>
> - err = os_seek_file(fd, offset);
> - if (err < 0)
> - return err;
> -
> - err = os_read_file(fd, buf, len);
> + err = os_pread_file(fd, buf, len, offset);
> if (err < 0)
> return err;
>
> @@ -1377,14 +1373,8 @@ static int update_bitmap(struct io_thread_req *req)
> if(req->cow_offset == -1)
> return 0;
>
> - n = os_seek_file(req->fds[1], req->cow_offset);
> - if(n < 0){
> - printk("do_io - bitmap lseek failed : err = %d\n", -n);
> - return 1;
> - }
> -
> - n = os_write_file(req->fds[1], &req->bitmap_words,
> - sizeof(req->bitmap_words));
> + n = os_pwrite_file(req->fds[1], &req->bitmap_words,
> + sizeof(req->bitmap_words), req->cow_offset);
> if(n != sizeof(req->bitmap_words)){
> printk("do_io - bitmap update failed, err = %d fd = %d\n", -n,
> req->fds[1]);
> @@ -1399,7 +1389,6 @@ static void do_io(struct io_thread_req *req)
> char *buf;
> unsigned long len;
> int n, nsectors, start, end, bit;
> - int err;
> __u64 off;
>
> if (req->op == UBD_FLUSH) {
> @@ -1428,18 +1417,12 @@ static void do_io(struct io_thread_req *req)
> len = (end - start) * req->sectorsize;
> buf = &req->buffer[start * req->sectorsize];
>
> - err = os_seek_file(req->fds[bit], off);
> - if(err < 0){
> - printk("do_io - lseek failed : err = %d\n", -err);
> - req->error = 1;
> - return;
> - }
> if(req->op == UBD_READ){
> n = 0;
> do {
> buf = &buf[n];
> len -= n;
> - n = os_read_file(req->fds[bit], buf, len);
> + n = os_pread_file(req->fds[bit], buf, len, off);
> if (n < 0) {
> printk("do_io - read failed, err = %d "
> "fd = %d\n", -n, req->fds[bit]);
> @@ -1449,7 +1432,7 @@ static void do_io(struct io_thread_req *req)
> } while((n < len) && (n != 0));
> if (n < len) memset(&buf[n], 0, len - n);
> } else {
> - n = os_write_file(req->fds[bit], buf, len);
> + n = os_pwrite_file(req->fds[bit], buf, len, off);
> if(n != len){
> printk("do_io - write failed err = %d "
> "fd = %d\n", -n, req->fds[bit]);
> diff --git a/arch/um/include/shared/os.h b/arch/um/include/shared/os.h
> index 21d704b..de5d572 100644
> --- a/arch/um/include/shared/os.h
> +++ b/arch/um/include/shared/os.h
> @@ -146,6 +146,8 @@ extern int os_read_file(int fd, void *buf, int len);
> extern int os_write_file(int fd, const void *buf, int count);
> extern int os_sync_file(int fd);
> extern int os_file_size(const char *file, unsigned long long *size_out);
> +extern int os_pread_file(int fd, void *buf, int len, unsigned long long
> offset);
> +extern int os_pwrite_file(int fd, const void *buf, int count, unsigned long
> long offset);
> extern int os_file_modtime(const char *file, unsigned long *modtime);
> extern int os_pipe(int *fd, int stream, int close_on_exec);
> extern int os_set_fd_async(int fd);
> diff --git a/arch/um/os-Linux/file.c b/arch/um/os-Linux/file.c
> index 26e0164..2db18cb 100644
> --- a/arch/um/os-Linux/file.c
> +++ b/arch/um/os-Linux/file.c
> @@ -264,6 +264,15 @@ int os_read_file(int fd, void *buf, int len)
> return n;
> }
>
> +int os_pread_file(int fd, void *buf, int len, unsigned long long offset)
> +{
> + int n = pread(fd, buf, len, offset);
> +
> + if (n < 0)
> + return -errno;
> + return n;
> +}
> +
> int os_write_file(int fd, const void *buf, int len)
> {
> int n = write(fd, (void *) buf, len);
> @@ -282,6 +291,16 @@ int os_sync_file(int fd)
> return n;
> }
>
> +int os_pwrite_file(int fd, const void *buf, int len, unsigned long long
> offset)
> +{
> + int n = pwrite(fd, (void *) buf, len, offset);
> +
> + if (n < 0)
> + return -errno;
> + return n;
> +}
> +
> +
> int os_file_size(const char *file, unsigned long long *size_out)
> {
> struct uml_stat buf;
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