[RFC PATCH v2] virtio/vsock: allocate multiple skbuffs on tx

[RFC PATCH v2] virtio/vsock: allocate multiple skbuffs on tx

[Arseniy Krasnov]

This adds small optimization for tx path: instead of allocating single
skbuff on every call to transport, allocate multiple skbuff's until
credit space allows, thus trying to send as much as possible data without
return to af_vsock.c.

Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
---
 Link to v1:
 https://lore.kernel.org/netdev/2c52aa26-8181-d37a-bccd-a86bd3cbc6e1@sberdevices.ru/

 Changelog:
 v1 -> v2:
 - If sent something, return number of bytes sent (even in
   case of error). Return error only if failed to sent first
   skbuff.

 net/vmw_vsock/virtio_transport_common.c | 53 ++++++++++++++++++-------
 1 file changed, 39 insertions(+), 14 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 6564192e7f20..3fdf1433ec28 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -196,7 +196,8 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 	const struct virtio_transport *t_ops;
 	struct virtio_vsock_sock *vvs;
 	u32 pkt_len = info->pkt_len;
-	struct sk_buff *skb;
+	u32 rest_len;
+	int ret;
 
 	info->type = virtio_transport_get_type(sk_vsock(vsk));
 
@@ -216,10 +217,6 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 
 	vvs = vsk->trans;
 
-	/* we can send less than pkt_len bytes */
-	if (pkt_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
-		pkt_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
-
 	/* virtio_transport_get_credit might return less than pkt_len credit */
 	pkt_len = virtio_transport_get_credit(vvs, pkt_len);
 
@@ -227,17 +224,45 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 	if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW)
 		return pkt_len;
 
-	skb = virtio_transport_alloc_skb(info, pkt_len,
-					 src_cid, src_port,
-					 dst_cid, dst_port);
-	if (!skb) {
-		virtio_transport_put_credit(vvs, pkt_len);
-		return -ENOMEM;
-	}
+	ret = 0;
+	rest_len = pkt_len;
+
+	do {
+		struct sk_buff *skb;
+		size_t skb_len;
+
+		skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE, rest_len);
+
+		skb = virtio_transport_alloc_skb(info, skb_len,
+						 src_cid, src_port,
+						 dst_cid, dst_port);
+		if (!skb) {
+			ret = -ENOMEM;
+			break;
+		}
+
+		virtio_transport_inc_tx_pkt(vvs, skb);
+
+		ret = t_ops->send_pkt(skb);
+
+		if (ret < 0)
+			break;
 
-	virtio_transport_inc_tx_pkt(vvs, skb);
+		rest_len -= skb_len;
+	} while (rest_len);
 
-	return t_ops->send_pkt(skb);
+	/* Don't call this function with zero as argument:
+	 * it tries to acquire spinlock and such argument
+	 * makes this call useless.
+	 */
+	if (rest_len)
+		virtio_transport_put_credit(vvs, rest_len);
+
+	/* Return number of bytes, if any data has been sent. */
+	if (rest_len != pkt_len)
+		ret = pkt_len - rest_len;
+
+	return ret;
 }
 
 static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
-- 
2.25.1

Re: [RFC PATCH v2] virtio/vsock: allocate multiple skbuffs on tx

[Stefano Garzarella]

On Sun, Mar 19, 2023 at 09:46:10PM +0300, Arseniy Krasnov wrote:
>This adds small optimization for tx path: instead of allocating single
>skbuff on every call to transport, allocate multiple skbuff's until
>credit space allows, thus trying to send as much as possible data without
>return to af_vsock.c.
>
>Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
>---
> Link to v1:
> https://lore.kernel.org/netdev/2c52aa26-8181-d37a-bccd-a86bd3cbc6e1@sberdevices.ru/
>
> Changelog:
> v1 -> v2:
> - If sent something, return number of bytes sent (even in
>   case of error). Return error only if failed to sent first
>   skbuff.
>
> net/vmw_vsock/virtio_transport_common.c | 53 ++++++++++++++++++-------
> 1 file changed, 39 insertions(+), 14 deletions(-)
>
>diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>index 6564192e7f20..3fdf1433ec28 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -196,7 +196,8 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
> 	const struct virtio_transport *t_ops;
> 	struct virtio_vsock_sock *vvs;
> 	u32 pkt_len = info->pkt_len;
>-	struct sk_buff *skb;
>+	u32 rest_len;
>+	int ret;
>
> 	info->type = virtio_transport_get_type(sk_vsock(vsk));
>
>@@ -216,10 +217,6 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>
> 	vvs = vsk->trans;
>
>-	/* we can send less than pkt_len bytes */
>-	if (pkt_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
>-		pkt_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
>-
> 	/* virtio_transport_get_credit might return less than pkt_len credit */
> 	pkt_len = virtio_transport_get_credit(vvs, pkt_len);
>
>@@ -227,17 +224,45 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
> 	if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW)
> 		return pkt_len;
>
>-	skb = virtio_transport_alloc_skb(info, pkt_len,
>-					 src_cid, src_port,
>-					 dst_cid, dst_port);
>-	if (!skb) {
>-		virtio_transport_put_credit(vvs, pkt_len);
>-		return -ENOMEM;
>-	}
>+	ret = 0;
>+	rest_len = pkt_len;
>+
>+	do {
>+		struct sk_buff *skb;
>+		size_t skb_len;
>+
>+		skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE, rest_len);
>+
>+		skb = virtio_transport_alloc_skb(info, skb_len,
>+						 src_cid, src_port,
>+						 dst_cid, dst_port);
>+		if (!skb) {
>+			ret = -ENOMEM;
>+			break;
>+		}
>+
>+		virtio_transport_inc_tx_pkt(vvs, skb);
>+
>+		ret = t_ops->send_pkt(skb);
>+
>+		if (ret < 0)
>+			break;
>
>-	virtio_transport_inc_tx_pkt(vvs, skb);
>+		rest_len -= skb_len;

t_ops->send_pkt() is returning the number of bytes sent. Current
implementations always return `skb_len`, so there should be no problem,
but it would be better to put a comment here, or we should handle the
case where ret != skb_len to avoid future issues.

>+	} while (rest_len);
>
>-	return t_ops->send_pkt(skb);
>+	/* Don't call this function with zero as argument:
>+	 * it tries to acquire spinlock and such argument
>+	 * makes this call useless.

Good point, can we do the same also for virtio_transport_get_credit()?
(Maybe in a separate patch)

I'm thinking if may be better to do it directly inside the functions,
but I don't have a strong opinion on that since we only call them here.

Thanks,
Stefano

>+	 */
>+	if (rest_len)
>+		virtio_transport_put_credit(vvs, rest_len);
>+
>+	/* Return number of bytes, if any data has been sent. */
>+	if (rest_len != pkt_len)
>+		ret = pkt_len - rest_len;
>+
>+	return ret;
> }
>
> static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
>-- 
>2.25.1
>

Re: [RFC PATCH v2] virtio/vsock: allocate multiple skbuffs on tx

[Arseniy Krasnov]

On 20.03.2023 17:29, Stefano Garzarella wrote:
> On Sun, Mar 19, 2023 at 09:46:10PM +0300, Arseniy Krasnov wrote:
>> This adds small optimization for tx path: instead of allocating single
>> skbuff on every call to transport, allocate multiple skbuff's until
>> credit space allows, thus trying to send as much as possible data without
>> return to af_vsock.c.
>>
>> Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
>> ---
>> Link to v1:
>> https://lore.kernel.org/netdev/2c52aa26-8181-d37a-bccd-a86bd3cbc6e1@sberdevices.ru/
>>
>> Changelog:
>> v1 -> v2:
>> - If sent something, return number of bytes sent (even in
>>   case of error). Return error only if failed to sent first
>>   skbuff.
>>
>> net/vmw_vsock/virtio_transport_common.c | 53 ++++++++++++++++++-------
>> 1 file changed, 39 insertions(+), 14 deletions(-)
>>
>> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>> index 6564192e7f20..3fdf1433ec28 100644
>> --- a/net/vmw_vsock/virtio_transport_common.c
>> +++ b/net/vmw_vsock/virtio_transport_common.c
>> @@ -196,7 +196,8 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>>     const struct virtio_transport *t_ops;
>>     struct virtio_vsock_sock *vvs;
>>     u32 pkt_len = info->pkt_len;
>> -    struct sk_buff *skb;
>> +    u32 rest_len;
>> +    int ret;
>>
>>     info->type = virtio_transport_get_type(sk_vsock(vsk));
>>
>> @@ -216,10 +217,6 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>>
>>     vvs = vsk->trans;
>>
>> -    /* we can send less than pkt_len bytes */
>> -    if (pkt_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
>> -        pkt_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
>> -
>>     /* virtio_transport_get_credit might return less than pkt_len credit */
>>     pkt_len = virtio_transport_get_credit(vvs, pkt_len);
>>
>> @@ -227,17 +224,45 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>>     if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW)
>>         return pkt_len;
>>
>> -    skb = virtio_transport_alloc_skb(info, pkt_len,
>> -                     src_cid, src_port,
>> -                     dst_cid, dst_port);
>> -    if (!skb) {
>> -        virtio_transport_put_credit(vvs, pkt_len);
>> -        return -ENOMEM;
>> -    }
>> +    ret = 0;
>> +    rest_len = pkt_len;
>> +
>> +    do {
>> +        struct sk_buff *skb;
>> +        size_t skb_len;
>> +
>> +        skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE, rest_len);
>> +
>> +        skb = virtio_transport_alloc_skb(info, skb_len,
>> +                         src_cid, src_port,
>> +                         dst_cid, dst_port);
>> +        if (!skb) {
>> +            ret = -ENOMEM;
>> +            break;
>> +        }
>> +
>> +        virtio_transport_inc_tx_pkt(vvs, skb);
>> +
>> +        ret = t_ops->send_pkt(skb);
>> +
>> +        if (ret < 0)
>> +            break;
>>
>> -    virtio_transport_inc_tx_pkt(vvs, skb);
>> +        rest_len -= skb_len;
> 
> t_ops->send_pkt() is returning the number of bytes sent. Current
> implementations always return `skb_len`, so there should be no problem,
> but it would be better to put a comment here, or we should handle the
> case where ret != skb_len to avoid future issues.

Hello, thanks for review!

I see. I think i'll handle such partial sends (ret != skb_len) as error, as
it is the only thing to do - we remove 'skb_len' from user's buffer, but
'send_pkt()' returns another value, so it will be strange for me to continue
this tx loop as everything is ok. Something like this:
+ 
+ if (ret < 0)
+    break;
+ 
+ if (ret != skb_len) {
+    ret = -EFAULT;//or may be -EIO
+    break;
+ }

> 
>> +    } while (rest_len);
>>
>> -    return t_ops->send_pkt(skb);
>> +    /* Don't call this function with zero as argument:
>> +     * it tries to acquire spinlock and such argument
>> +     * makes this call useless.
> 
> Good point, can we do the same also for virtio_transport_get_credit()?
> (Maybe in a separate patch)
> 
> I'm thinking if may be better to do it directly inside the functions,
> but I don't have a strong opinion on that since we only call them here.
> 

I think in this patch i can call 'virtio_transport_put_credit()' without if, but
i'll prepare separate patch which adds zero argument check to this function.
As i see, the only function suitable for such 'if' condition is 'virtio_transport_put_credit()'.
Anyway - for future use this check won't be bad.

Thanks, Arseniy

> Thanks,
> Stefano
> 
>> +     */
>> +    if (rest_len)
>> +        virtio_transport_put_credit(vvs, rest_len);
>> +
>> +    /* Return number of bytes, if any data has been sent. */
>> +    if (rest_len != pkt_len)
>> +        ret = pkt_len - rest_len;
>> +
>> +    return ret;
>> }
>>
>> static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
>> -- 
>> 2.25.1
>>
> 

Re: [RFC PATCH v2] virtio/vsock: allocate multiple skbuffs on tx

[Stefano Garzarella]

On Mon, Mar 20, 2023 at 09:02:19PM +0300, Arseniy Krasnov wrote:
>
>
>On 20.03.2023 17:29, Stefano Garzarella wrote:
>> On Sun, Mar 19, 2023 at 09:46:10PM +0300, Arseniy Krasnov wrote:
>>> This adds small optimization for tx path: instead of allocating single
>>> skbuff on every call to transport, allocate multiple skbuff's until
>>> credit space allows, thus trying to send as much as possible data without
>>> return to af_vsock.c.
>>>
>>> Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
>>> ---
>>> Link to v1:
>>> https://lore.kernel.org/netdev/2c52aa26-8181-d37a-bccd-a86bd3cbc6e1@sberdevices.ru/
>>>
>>> Changelog:
>>> v1 -> v2:
>>> - If sent something, return number of bytes sent (even in
>>>   case of error). Return error only if failed to sent first
>>>   skbuff.
>>>
>>> net/vmw_vsock/virtio_transport_common.c | 53 ++++++++++++++++++-------
>>> 1 file changed, 39 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>>> index 6564192e7f20..3fdf1433ec28 100644
>>> --- a/net/vmw_vsock/virtio_transport_common.c
>>> +++ b/net/vmw_vsock/virtio_transport_common.c
>>> @@ -196,7 +196,8 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>>>     const struct virtio_transport *t_ops;
>>>     struct virtio_vsock_sock *vvs;
>>>     u32 pkt_len = info->pkt_len;
>>> -    struct sk_buff *skb;
>>> +    u32 rest_len;
>>> +    int ret;
>>>
>>>     info->type = virtio_transport_get_type(sk_vsock(vsk));
>>>
>>> @@ -216,10 +217,6 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>>>
>>>     vvs = vsk->trans;
>>>
>>> -    /* we can send less than pkt_len bytes */
>>> -    if (pkt_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
>>> -        pkt_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
>>> -
>>>     /* virtio_transport_get_credit might return less than pkt_len credit */
>>>     pkt_len = virtio_transport_get_credit(vvs, pkt_len);
>>>
>>> @@ -227,17 +224,45 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
>>>     if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW)
>>>         return pkt_len;
>>>
>>> -    skb = virtio_transport_alloc_skb(info, pkt_len,
>>> -                     src_cid, src_port,
>>> -                     dst_cid, dst_port);
>>> -    if (!skb) {
>>> -        virtio_transport_put_credit(vvs, pkt_len);
>>> -        return -ENOMEM;
>>> -    }
>>> +    ret = 0;
>>> +    rest_len = pkt_len;
>>> +
>>> +    do {
>>> +        struct sk_buff *skb;
>>> +        size_t skb_len;
>>> +
>>> +        skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE, rest_len);
>>> +
>>> +        skb = virtio_transport_alloc_skb(info, skb_len,
>>> +                         src_cid, src_port,
>>> +                         dst_cid, dst_port);
>>> +        if (!skb) {
>>> +            ret = -ENOMEM;
>>> +            break;
>>> +        }
>>> +
>>> +        virtio_transport_inc_tx_pkt(vvs, skb);
>>> +
>>> +        ret = t_ops->send_pkt(skb);
>>> +
>>> +        if (ret < 0)
>>> +            break;
>>>
>>> -    virtio_transport_inc_tx_pkt(vvs, skb);
>>> +        rest_len -= skb_len;
>>
>> t_ops->send_pkt() is returning the number of bytes sent. Current
>> implementations always return `skb_len`, so there should be no problem,
>> but it would be better to put a comment here, or we should handle the
>> case where ret != skb_len to avoid future issues.
>
>Hello, thanks for review!
>
>I see. I think i'll handle such partial sends (ret != skb_len) as error, as
>it is the only thing to do - we remove 'skb_len' from user's buffer, but
>'send_pkt()' returns another value, so it will be strange for me to continue
>this tx loop as everything is ok. Something like this:
>+
>+ if (ret < 0)
>+    break;
>+
>+ if (ret != skb_len) {
>+    ret = -EFAULT;//or may be -EIO
>+    break;
>+ }

Good for me.

>
>>
>>> +    } while (rest_len);
>>>
>>> -    return t_ops->send_pkt(skb);
>>> +    /* Don't call this function with zero as argument:
>>> +     * it tries to acquire spinlock and such argument
>>> +     * makes this call useless.
>>
>> Good point, can we do the same also for virtio_transport_get_credit()?
>> (Maybe in a separate patch)
>>
>> I'm thinking if may be better to do it directly inside the functions,
>> but I don't have a strong opinion on that since we only call them here.
>>
>
>I think in this patch i can call 'virtio_transport_put_credit()' without if, but
>i'll prepare separate patch which adds zero argument check to this function.

Yep, I agree.

>As i see, the only function suitable for such 'if' condition is
>'virtio_transport_put_credit()'.

Why not even for virtio_transport_get_credit() ?

When we send packets without payload (e.g. VIRTIO_VSOCK_OP_REQUEST,
VIRTIO_VSOCK_OP_SHUTDOWN) we call virtio_transport_get_credit()
with `credit` parameter equal to 0, then we acquire the spinlock but
in the end we do nothing.

>Anyway - for future use this check won't be bad.

Yep, these are minor improvements ;-)

Thanks,
Stefano