Re: [uml-devel] [PATCH] Update UBD to use pread/pwrite family of functions

[Anton Ivanov <anton.ivanov@kot-begemot.co.uk>]

Hi list, hi Richard.

Have you had time to review this one? I think it is not contentious - it 
is something QEMU has been doing for a very long time now. It also gives 
a measurable speed up, especially for random IO.

I am going to hold off on the rest of the ubd patches because they bulk 
up the transactions. This is dangerous if you end up in a reentrant 
situation.

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 <aivanov@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;


------------------------------------------------------------------------------
_______________________________________________
User-mode-linux-devel mailing list
User-mode-linux-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel