Re: [PATCH net-next v8 0/4] vsock/virtio/vhost: MSG_ZEROCOPY preparations

[Arseniy Krasnov <avkrasnov@salutedevices.com>]

On 14.09.2023 18:34, Stefano Garzarella wrote:
> On Thu, Sep 14, 2023 at 05:05:17PM +0300, Arseniy Krasnov wrote:
>> Hello Stefano,
>>
>> On 14.09.2023 17:07, Stefano Garzarella wrote:
>>> Hi Arseniy,
>>>
>>> On Mon, Sep 11, 2023 at 11:22:30PM +0300, Arseniy Krasnov wrote:
>>>> Hello,
>>>>
>>>> this patchset is first of three parts of another big patchset for
>>>> MSG_ZEROCOPY flag support:
>>>> https://lore.kernel.org/netdev/20230701063947.3422088-1-AVKrasnov@sberdevices.ru/
>>>>
>>>> During review of this series, Stefano Garzarella <sgarzare@redhat.com>
>>>> suggested to split it for three parts to simplify review and merging:
>>>>
>>>> 1) virtio and vhost updates (for fragged skbs) <--- this patchset
>>>> 2) AF_VSOCK updates (allows to enable MSG_ZEROCOPY mode and read
>>>>   tx completions) and update for Documentation/.
>>>> 3) Updates for tests and utils.
>>>>
>>>> This series enables handling of fragged skbs in virtio and vhost parts.
>>>> Newly logic won't be triggered, because SO_ZEROCOPY options is still
>>>> impossible to enable at this moment (next bunch of patches from big
>>>> set above will enable it).
>>>>
>>>> I've included changelog to some patches anyway, because there were some
>>>> comments during review of last big patchset from the link above.
>>>
>>> Thanks, I left some comments on patch 4, the others LGTM.
>>> Sorry to not having spotted them before, but moving
>>> virtio_transport_alloc_skb() around the file, made the patch a little
>>> confusing and difficult to review.
>>
>> Sure, no problem, I'll fix them! Thanks for review.
>>
>>>
>>> In addition, I started having failures of test 14 (server: host,
>>> client: guest), so I looked better to see if there was anything wrong,
>>> but it fails me even without this series applied.
>>>
>>> It happens to me intermittently (~30%), does it happen to you?
>>> Can you take a look at it?
>>
>> Yes! sometime ago I also started to get fails of this test, not ~30%,
>> significantly rare, but it depends on environment I guess, anyway I'm going to
>> look at this on the next few days
> 
> Maybe it's just a timing issue in the test, indeed we are expecting 8
> bytes but we received only 3 plus the 2 bytes we received before it
> seems exactly the same bytes we send with the first
> `send(fd, HELLO_STR, strlen(HELLO_STR), 0);`
> 
> Since it is a stream socket, it could happen, so we should retry
> the recv() or just use MSG_WAITALL.
> 
> Applying the following patch fixed the issue for me (15 mins without
> errors for now):
> 
> diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
> index 90718c2fd4ea..7b0fed9fc58d 100644
> --- a/tools/testing/vsock/vsock_test.c
> +++ b/tools/testing/vsock/vsock_test.c
> @@ -1129,7 +1129,7 @@ static void test_stream_virtio_skb_merge_server(const struct test_opts *opts)
>         control_expectln("SEND0");
> 
>         /* Read skbuff partially. */
> -       res = recv(fd, buf, 2, 0);
> +       res = recv(fd, buf, 2, MSG_WAITALL);
>         if (res != 2) {
>                 fprintf(stderr, "expected recv(2) returns 2 bytes, got %zi\n", res);
>                 exit(EXIT_FAILURE);
> @@ -1138,7 +1138,7 @@ static void test_stream_virtio_skb_merge_server(const struct test_opts *opts)
>         control_writeln("REPLY0");
>         control_expectln("SEND1");
> 
> -       res = recv(fd, buf + 2, sizeof(buf) - 2, 0);
> +       res = recv(fd, buf + 2, 8, MSG_WAITALL);
>         if (res != 8) {
>                 fprintf(stderr, "expected recv(2) returns 8 bytes, got %zi\n", res);
>                 exit(EXIT_FAILURE);
> 
> I will check better all the cases and send a patch upstream.

Agree, I think this will fix it!

Thanks, Arseniy

> 
> Anyway it looks just an issue in our test suite :-)
> 
> Stefano
> 
>>
>> Thanks, Arseniy
>>
>>>
>>> host$ ./vsock_test --mode=server --control-port=12345 --peer-cid=4
>>> ...
>>> 14 - SOCK_STREAM virtio skb merge...expected recv(2) returns 8 bytes, got 3
>>>
>>> guest$ ./vsock_test --mode=client --control-host=192.168.133.2 --control-port=12345 --peer-cid=2
>>>
>>> Thanks,
>>> Stefano
>>>
>>
>