Message-ID: <CAHS8izNwpgf3ks1C6SCqDhUPnR=mbo-AdE2kQ3yk4HK-tFUUhg@mail.gmail.com>
Date: Wed, 21 May 2025 10:21:06 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Stanislav Fomichev <stfomichev@...il.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com, 
	kuba@...nel.org, pabeni@...hat.com, viro@...iv.linux.org.uk, horms@...nel.org, 
	andrew+netdev@...n.ch, shuah@...nel.org, sagi@...mberg.me, willemb@...gle.com, 
	asml.silence@...il.com, jdamato@...tly.com, kaiyuanz@...gle.com, 
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net-next 2/3] selftests: ncdevmem: make chunking optional

On Tue, May 20, 2025 at 1:30 PM Stanislav Fomichev <stfomichev@...il.com> wrote:
>
> Add new -z argument to specify max IOV size. By default, use
> single large IOV.
>
> Signed-off-by: Stanislav Fomichev <stfomichev@...il.com>
> ---
>  .../selftests/drivers/net/hw/ncdevmem.c       | 49 +++++++++++--------
>  1 file changed, 29 insertions(+), 20 deletions(-)
>
> diff --git a/tools/testing/selftests/drivers/net/hw/ncdevmem.c b/tools/testing/selftests/drivers/net/hw/ncdevmem.c
> index ca723722a810..fc7ba7d71502 100644
> --- a/tools/testing/selftests/drivers/net/hw/ncdevmem.c
> +++ b/tools/testing/selftests/drivers/net/hw/ncdevmem.c
> @@ -82,6 +82,9 @@
>  #define MSG_SOCK_DEVMEM 0x2000000
>  #endif
>
> +#define MAX_IOV 1024
> +
> +static size_t max_chunk;
>  static char *server_ip;
>  static char *client_ip;
>  static char *port;
> @@ -834,10 +837,10 @@ static int do_client(struct memory_buffer *mem)
>         struct sockaddr_in6 server_sin;
>         struct sockaddr_in6 client_sin;
>         struct ynl_sock *ys = NULL;
> +       struct iovec iov[MAX_IOV];
>         struct msghdr msg = {};
>         ssize_t line_size = 0;
>         struct cmsghdr *cmsg;
> -       struct iovec iov[2];
>         char *line = NULL;
>         unsigned long mid;
>         size_t len = 0;
> @@ -893,27 +896,29 @@ static int do_client(struct memory_buffer *mem)
>                 if (line_size < 0)
>                         break;
>
> -               mid = (line_size / 2) + 1;
> -
> -               iov[0].iov_base = (void *)1;
> -               iov[0].iov_len = mid;
> -               iov[1].iov_base = (void *)(mid + 2);
> -               iov[1].iov_len = line_size - mid;
> +               if (max_chunk) {
> +                       msg.msg_iovlen =
> +                               (line_size + max_chunk - 1) / max_chunk;
> +                       if (msg.msg_iovlen > MAX_IOV)
> +                               error(1, 0,
> +                                     "can't partition %zd bytes into maximum of %d chunks",
> +                                     line_size, MAX_IOV);
>
> -               provider->memcpy_to_device(mem, (size_t)iov[0].iov_base, line,
> -                                          iov[0].iov_len);
> -               provider->memcpy_to_device(mem, (size_t)iov[1].iov_base,
> -                                          line + iov[0].iov_len,
> -                                          iov[1].iov_len);
> +                       for (int i = 0; i < msg.msg_iovlen; i++) {
> +                               iov[i].iov_base = (void *)(i * max_chunk);
> +                               iov[i].iov_len = max_chunk;

Isn't the last iov going to be truncated in the case where line_size
is not exactly divisible with max_chunk?

> +                       }
>
> -               fprintf(stderr,
> -                       "read line_size=%ld iov[0].iov_base=%lu, iov[0].iov_len=%lu, iov[1].iov_base=%lu, iov[1].iov_len=%lu\n",
> -                       line_size, (unsigned long)iov[0].iov_base,
> -                       iov[0].iov_len, (unsigned long)iov[1].iov_base,
> -                       iov[1].iov_len);
> +                       iov[msg.msg_iovlen - 1].iov_len =
> +                               line_size - (msg.msg_iovlen - 1) * max_chunk;
> +               } else {
> +                       iov[0].iov_base = 0;
> +                       iov[0].iov_len = line_size;
> +                       msg.msg_iovlen = 1;
> +               }

Do you need to special case this? Shouldn't this be the same as max_chunk==1?

>
>                 msg.msg_iov = iov;
> -               msg.msg_iovlen = 2;
> +               provider->memcpy_to_device(mem, 0, line, line_size);
>
>                 msg.msg_control = ctrl_data;
>                 msg.msg_controllen = sizeof(ctrl_data);
> @@ -934,7 +939,8 @@ static int do_client(struct memory_buffer *mem)
>                 fprintf(stderr, "sendmsg_ret=%d\n", ret);
>
>                 if (ret != line_size)
> -                       error(1, errno, "Did not send all bytes");
> +                       error(1, errno, "Did not send all bytes %d vs %zd", ret,
> +                             line_size);
>
>                 wait_compl(socket_fd);
>         }
> @@ -956,7 +962,7 @@ int main(int argc, char *argv[])
>         int is_server = 0, opt;
>         int ret;
>
> -       while ((opt = getopt(argc, argv, "ls:c:p:v:q:t:f:")) != -1) {
> +       while ((opt = getopt(argc, argv, "ls:c:p:v:q:t:f:z:")) != -1) {
>                 switch (opt) {
>                 case 'l':
>                         is_server = 1;
> @@ -982,6 +988,9 @@ int main(int argc, char *argv[])
>                 case 'f':
>                         ifname = optarg;
>                         break;
> +               case 'z':
> +                       max_chunk = atoi(optarg);
> +                       break;
>                 case '?':
>                         fprintf(stderr, "unknown option: %c\n", optopt);
>                         break;
> --
> 2.49.0
>


-- 
Thanks,
Mina

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