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Message-ID: <15bae73e-e753-123a-7535-0ab5c1178b40@iogearbox.net>
Date: Fri, 27 Nov 2020 22:29:37 +0100
From: Daniel Borkmann <daniel@...earbox.net>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, magnus.karlsson@...il.com
Cc: Björn Töpel <bjorn.topel@...el.com>,
Magnus Karlsson <magnus.karlsson@...el.com>,
Jonathan Lemon <jonathan.lemon@...il.com>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Alexei Starovoitov <ast@...nel.org>,
Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...il.com>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
Andrii Nakryiko <andrii@...nel.org>,
KP Singh <kpsingh@...omium.org>,
"open list:XDP SOCKETS (AF_XDP)" <netdev@...r.kernel.org>,
"open list:XDP SOCKETS (AF_XDP)" <bpf@...r.kernel.org>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf v2 2/2] xsk: change the tx writeable condition
On 11/25/20 7:48 AM, Xuan Zhuo wrote:
> Modify the tx writeable condition from the queue is not full to the
> number of present tx queues is less than the half of the total number
> of queues. Because the tx queue not full is a very short time, this will
> cause a large number of EPOLLOUT events, and cause a large number of
> process wake up.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
This one doesn't apply cleanly against bpf tree, please rebase. Small comment
inline while looking over the patch:
> ---
> net/xdp/xsk.c | 16 +++++++++++++---
> net/xdp/xsk_queue.h | 6 ++++++
> 2 files changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 0df8651..22e35e9 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -211,6 +211,14 @@ static int __xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len,
> return 0;
> }
>
> +static bool xsk_tx_writeable(struct xdp_sock *xs)
> +{
> + if (xskq_cons_present_entries(xs->tx) > xs->tx->nentries / 2)
> + return false;
> +
> + return true;
> +}
> +
> static bool xsk_is_bound(struct xdp_sock *xs)
> {
> if (READ_ONCE(xs->state) == XSK_BOUND) {
> @@ -296,7 +304,8 @@ void xsk_tx_release(struct xsk_buff_pool *pool)
> rcu_read_lock();
> list_for_each_entry_rcu(xs, &pool->xsk_tx_list, tx_list) {
> __xskq_cons_release(xs->tx);
> - xs->sk.sk_write_space(&xs->sk);
> + if (xsk_tx_writeable(xs))
> + xs->sk.sk_write_space(&xs->sk);
> }
> rcu_read_unlock();
> }
> @@ -499,7 +508,8 @@ static int xsk_generic_xmit(struct sock *sk)
>
> out:
> if (sent_frame)
> - sk->sk_write_space(sk);
> + if (xsk_tx_writeable(xs))
> + sk->sk_write_space(sk);
>
> mutex_unlock(&xs->mutex);
> return err;
> @@ -556,7 +566,7 @@ static __poll_t xsk_poll(struct file *file, struct socket *sock,
>
> if (xs->rx && !xskq_prod_is_empty(xs->rx))
> mask |= EPOLLIN | EPOLLRDNORM;
> - if (xs->tx && !xskq_cons_is_full(xs->tx))
> + if (xs->tx && xsk_tx_writeable(xs))
> mask |= EPOLLOUT | EPOLLWRNORM;
>
> return mask;
> diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
> index b936c46..b655004 100644
> --- a/net/xdp/xsk_queue.h
> +++ b/net/xdp/xsk_queue.h
> @@ -307,6 +307,12 @@ static inline bool xskq_cons_is_full(struct xsk_queue *q)
> q->nentries;
> }
>
> +static inline __u64 xskq_cons_present_entries(struct xsk_queue *q)
Types prefixed with __ are mainly for user-space facing things like uapi headers,
so in-kernel should be u64. Is there a reason this is not done as u32 (and thus
same as producer and producer)?
> +{
> + /* No barriers needed since data is not accessed */
> + return READ_ONCE(q->ring->producer) - READ_ONCE(q->ring->consumer);
> +}
> +
> /* Functions for producers */
>
> static inline u32 xskq_prod_nb_free(struct xsk_queue *q, u32 max)
>
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