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Message-ID: <99935734-4006-509f-5e02-3229f0847b67@salutedevices.com>
Date:   Fri, 17 Nov 2023 10:10:08 +0300
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Subject: Re: [RFC PATCH v1 1/2] virtio/vsock: send credit update during
 setting SO_RCVLOWAT
To:     Stefano Garzarella <sgarzare@redhat.com>
CC:     Stefan Hajnoczi <stefanha@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Bobby Eshleman <bobby.eshleman@bytedance.com>,
        <kvm@vger.kernel.org>, <virtualization@lists.linux-foundation.org>,
        <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <kernel@sberdevices.ru>, <oxffffaa@gmail.com>
References: <20231108072004.1045669-1-avkrasnov@salutedevices.com>
 <20231108072004.1045669-2-avkrasnov@salutedevices.com>
 <6owgy5zo5lmx3w2vsu6ux552olyuq4lnqzrawngc3gmi5fonn6@6emsez7krq7f>
Content-Language: en-US
From:   Arseniy Krasnov <avkrasnov@salutedevices.com>
In-Reply-To: <6owgy5zo5lmx3w2vsu6ux552olyuq4lnqzrawngc3gmi5fonn6@6emsez7krq7f>
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On 15.11.2023 14:08, Stefano Garzarella wrote:
> On Wed, Nov 08, 2023 at 10:20:03AM +0300, Arseniy Krasnov wrote:
>> This adds sending credit update message when SO_RCVLOWAT is updated and
>> it is bigger than number of bytes in rx queue. It is needed, because
>> 'poll()' will wait until number of bytes in rx queue will be not smaller
>> than SO_RCVLOWAT, so kick sender to send more data. Otherwise mutual
>> hungup for tx/rx is possible: sender waits for free space and receiver
>> is waiting data in 'poll()'.
>>
>> Signed-off-by: Arseniy Krasnov <avkrasnov@salutedevices.com>
>> ---
>> drivers/vhost/vsock.c                   |  2 ++
>> include/linux/virtio_vsock.h            |  1 +
>> net/vmw_vsock/virtio_transport.c        |  2 ++
>> net/vmw_vsock/virtio_transport_common.c | 31 +++++++++++++++++++++++++
>> net/vmw_vsock/vsock_loopback.c          |  2 ++
>> 5 files changed, 38 insertions(+)
>>
>> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
>> index f75731396b7e..ecfa5c11f5ee 100644
>> --- a/drivers/vhost/vsock.c
>> +++ b/drivers/vhost/vsock.c
>> @@ -451,6 +451,8 @@ static struct virtio_transport vhost_transport = {
>>         .notify_buffer_size       = virtio_transport_notify_buffer_size,
>>
>>         .read_skb = virtio_transport_read_skb,
>> +
>> +        .set_rcvlowat             = virtio_transport_set_rcvlowat
>>     },
>>
>>     .send_pkt = vhost_transport_send_pkt,
>> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
>> index ebb3ce63d64d..97dc1bebc69c 100644
>> --- a/include/linux/virtio_vsock.h
>> +++ b/include/linux/virtio_vsock.h
>> @@ -256,4 +256,5 @@ void virtio_transport_put_credit(struct virtio_vsock_sock *vvs, u32 credit);
>> void virtio_transport_deliver_tap_pkt(struct sk_buff *skb);
>> int virtio_transport_purge_skbs(void *vsk, struct sk_buff_head *list);
>> int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t read_actor);
>> +int virtio_transport_set_rcvlowat(struct vsock_sock *vsk, int val);
>> #endif /* _LINUX_VIRTIO_VSOCK_H */
>> diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
>> index af5bab1acee1..cf3431189d0c 100644
>> --- a/net/vmw_vsock/virtio_transport.c
>> +++ b/net/vmw_vsock/virtio_transport.c
>> @@ -539,6 +539,8 @@ static struct virtio_transport virtio_transport = {
>>         .notify_buffer_size       = virtio_transport_notify_buffer_size,
>>
>>         .read_skb = virtio_transport_read_skb,
>> +
>> +        .set_rcvlowat             = virtio_transport_set_rcvlowat
>>     },
>>
>>     .send_pkt = virtio_transport_send_pkt,
>> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>> index e22c81435ef7..88a58163046e 100644
>> --- a/net/vmw_vsock/virtio_transport_common.c
>> +++ b/net/vmw_vsock/virtio_transport_common.c
>> @@ -1676,6 +1676,37 @@ int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_acto
>> }
>> EXPORT_SYMBOL_GPL(virtio_transport_read_skb);
>>
>> +int virtio_transport_set_rcvlowat(struct vsock_sock *vsk, int val)
>> +{
>> +    struct virtio_vsock_sock *vvs = vsk->trans;
>> +    bool send_update = false;
> 
> I'd declare this not initialized.
> 
>> +
>> +    spin_lock_bh(&vvs->rx_lock);
>> +
>> +    /* If number of available bytes is less than new
>> +     * SO_RCVLOWAT value, kick sender to send more
>> +     * data, because sender may sleep in its 'send()'
>> +     * syscall waiting for enough space at our side.
>> +     */
>> +    if (vvs->rx_bytes < val)
>> +        send_update = true;
> 
> Then here just:
>     send_update = vvs->rx_bytes < val;
> 
>> +
>> +    spin_unlock_bh(&vvs->rx_lock);
>> +
>> +    if (send_update) {
>> +        int err;
>> +
>> +        err = virtio_transport_send_credit_update(vsk);
>> +        if (err < 0)
>> +            return err;
>> +    }
>> +
>> +    WRITE_ONCE(sk_vsock(vsk)->sk_rcvlowat, val ? : 1);
> 
> Not in this patch, but what about doing this in vsock_set_rcvlowat() in af_vsock.c?
> 
> I mean avoid to return if `transport->set_rcvlowat(vsk, val)` is
> successfully, so set sk_rcvlowat in a single point.

Yes, we can do it, I'll include new patch as 0001 in v2, don't remember why it wasn't implemented in this
way before.

Thanks, Arseniy

> 
> The rest LGTM!
> 
> Stefano
> 
>> +
>> +    return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(virtio_transport_set_rcvlowat);
>> +
>> MODULE_LICENSE("GPL v2");
>> MODULE_AUTHOR("Asias He");
>> MODULE_DESCRIPTION("common code for virtio vsock");
>> diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
>> index 048640167411..388c157f6633 100644
>> --- a/net/vmw_vsock/vsock_loopback.c
>> +++ b/net/vmw_vsock/vsock_loopback.c
>> @@ -98,6 +98,8 @@ static struct virtio_transport loopback_transport = {
>>         .notify_buffer_size       = virtio_transport_notify_buffer_size,
>>
>>         .read_skb = virtio_transport_read_skb,
>> +
>> +        .set_rcvlowat             = virtio_transport_set_rcvlowat
>>     },
>>
>>     .send_pkt = vsock_loopback_send_pkt,
>> -- 2.25.1
>>
>