[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <1b693647-bccf-48b3-8010-abdb91a32594@bytedance.com>
Date: Sat, 1 Jun 2024 15:52:24 -0700
From: Zijian Zhang <zijianzhang@...edance.com>
To: Simon Horman <horms@...nel.org>
Cc: netdev@...r.kernel.org, edumazet@...gle.com,
willemdebruijn.kernel@...il.com, cong.wang@...edance.com,
xiaochun.lu@...edance.com
Subject: Re: [External] Re: [PATCH net-next v4 2/3] sock: add MSG_ZEROCOPY
notification mechanism based on msg_control
On 6/1/24 3:37 AM, Simon Horman wrote:
> On Tue, May 28, 2024 at 09:21:02PM +0000, zijianzhang@...edance.com wrote:
>> From: Zijian Zhang <zijianzhang@...edance.com>
>>
>> The MSG_ZEROCOPY flag enables copy avoidance for socket send calls.
>> However, zerocopy is not a free lunch. Apart from the management of user
>> pages, the combination of poll + recvmsg to receive notifications incurs
>> unignorable overhead in the applications. The overhead of such sometimes
>> might be more than the CPU savings from zerocopy. We try to solve this
>> problem with a new notification mechanism based on msgcontrol.
>> This new mechanism aims to reduce the overhead associated with receiving
>> notifications by embedding them directly into user arguments passed with
>> each sendmsg control message. By doing so, we can significantly reduce
>> the complexity and overhead for managing notifications. In an ideal
>> pattern, the user will keep calling sendmsg with SCM_ZC_NOTIFICATION
>> msg_control, and the notification will be delivered as soon as possible.
>>
>> Signed-off-by: Zijian Zhang <zijianzhang@...edance.com>
>> Signed-off-by: Xiaochun Lu <xiaochun.lu@...edance.com>
>
> ...
>
>> diff --git a/net/core/sock.c b/net/core/sock.c
>> index 521e6373d4f7..21239469d75c 100644
>> --- a/net/core/sock.c
>> +++ b/net/core/sock.c
>> @@ -2847,6 +2847,74 @@ int __sock_cmsg_send(struct sock *sk, struct cmsghdr *cmsg,
>> case SCM_RIGHTS:
>> case SCM_CREDENTIALS:
>> break;
>> + case SCM_ZC_NOTIFICATION: {
>> + int ret, i = 0;
>> + int cmsg_data_len, zc_info_elem_num;
>> + void __user *usr_addr;
>> + struct zc_info_elem zc_info_kern[SOCK_ZC_INFO_MAX];
>> + unsigned long flags;
>> + struct sk_buff_head *q, local_q;
>> + struct sk_buff *skb, *tmp;
>> + struct sock_exterr_skb *serr;
>
> Hi Zijian Zhang, Xiaochun Lu, all,
>
> When compiling on ARM (32bit) with multi_v7_defconfig using clang-18
> I see the following warning:
>
> .../sock.c:2808:5: warning: stack frame size (1664) exceeds limit (1024) in '__sock_cmsg_send' [-Wframe-larger-than]
> 2808 | int __sock_cmsg_send(struct sock *sk, struct cmsghdr *cmsg,
>
> I expect this is mostly explained by the addition of zc_info_kern above.
>
Nice catch, thanks for the info!
>> +
>> + if (!sock_flag(sk, SOCK_ZEROCOPY) || sk->sk_family == PF_RDS)
>> + return -EINVAL;
>> +
>> + cmsg_data_len = cmsg->cmsg_len - sizeof(struct cmsghdr);
>> + if (cmsg_data_len % sizeof(struct zc_info_elem))
>> + return -EINVAL;
>> +
>> + zc_info_elem_num = cmsg_data_len / sizeof(struct zc_info_elem);
>> + if (!zc_info_elem_num || zc_info_elem_num > SOCK_ZC_INFO_MAX)
>> + return -EINVAL;
>> +
>> + if (in_compat_syscall())
>> + usr_addr = compat_ptr(*(compat_uptr_t *)CMSG_DATA(cmsg));
>> + else
>> + usr_addr = (void __user *)*(void **)CMSG_DATA(cmsg);
>> + if (!access_ok(usr_addr, cmsg_data_len))
>> + return -EFAULT;
>> +
>> + q = &sk->sk_error_queue;
>> + skb_queue_head_init(&local_q);
>> + spin_lock_irqsave(&q->lock, flags);
>> + skb = skb_peek(q);
>> + while (skb && i < zc_info_elem_num) {
>> + struct sk_buff *skb_next = skb_peek_next(skb, q);
>> +
>> + serr = SKB_EXT_ERR(skb);
>> + if (serr->ee.ee_errno == 0 &&
>> + serr->ee.ee_origin == SO_EE_ORIGIN_ZEROCOPY) {
>> + zc_info_kern[i].hi = serr->ee.ee_data;
>> + zc_info_kern[i].lo = serr->ee.ee_info;
>> + zc_info_kern[i].zerocopy = !(serr->ee.ee_code
>> + & SO_EE_CODE_ZEROCOPY_COPIED);
>> + __skb_unlink(skb, q);
>> + __skb_queue_tail(&local_q, skb);
>> + i++;
>> + }
>> + skb = skb_next;
>> + }
>> + spin_unlock_irqrestore(&q->lock, flags);
>> +
>> + ret = copy_to_user(usr_addr,
>> + zc_info_kern,
>> + i * sizeof(struct zc_info_elem));
>> +
>> + if (unlikely(ret)) {
>> + spin_lock_irqsave(&q->lock, flags);
>> + skb_queue_reverse_walk_safe(&local_q, skb, tmp) {
>> + __skb_unlink(skb, &local_q);
>> + __skb_queue_head(q, skb);
>> + }
>> + spin_unlock_irqrestore(&q->lock, flags);
>> + return -EFAULT;
>> + }
>> +
>> + while ((skb = __skb_dequeue(&local_q)))
>> + consume_skb(skb);
>> + break;
>> + }
>> default:
>> return -EINVAL;
>> }
>> --
>> 2.20.1
>>
>>
Powered by blists - more mailing lists