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Message-Id: <20231107214045.2172393-16-dw@davidwei.uk>
Date: Tue, 7 Nov 2023 13:40:40 -0800
From: David Wei <dw@...idwei.uk>
To: io-uring@...r.kernel.org,
netdev@...r.kernel.org
Cc: Jens Axboe <axboe@...nel.dk>,
Pavel Begunkov <asml.silence@...il.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jesper Dangaard Brouer <hawk@...nel.org>,
David Ahern <dsahern@...nel.org>,
Mina Almasry <almasrymina@...gle.com>,
Willem de Bruijn <willemdebruijn.kernel@...il.com>,
Dragos Tatulea <dtatulea@...dia.com>
Subject: [PATCH 15/20] io_uring/zcrx: add copy fallback
From: Pavel Begunkov <asml.silence@...il.com>
Currently, if user fails to keep up with the network and doesn't refill
the buffer ring fast enough the NIC/driver will start dropping packets.
That might be too punishing, so let's fall back to non-zerocopy version
by allowing the driver to do normal kernel allocations. Later, when
we're in the task context doing zc_rx_recv_skb() we'll detect such pages
and copy them into user specified buffers.
This patch implement the second (copy) part. It'll facilitate adoption
and help the user to strike the balance b/w allocation the right amount
of zerocopy buffers and being resilient to surges in traffic.
Note, due to technical reasons for now we're only using buffers from
->freelist, which is unreliably and is likely to fail with time. It'll
be revised in later patches.
Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
Signed-off-by: David Wei <dw@...idwei.uk>
---
io_uring/zc_rx.c | 115 ++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 105 insertions(+), 10 deletions(-)
diff --git a/io_uring/zc_rx.c b/io_uring/zc_rx.c
index c1502ec3e629..c2ed600f0951 100644
--- a/io_uring/zc_rx.c
+++ b/io_uring/zc_rx.c
@@ -498,6 +498,26 @@ static void io_zc_rx_refill_cache(struct io_zc_rx_ifq *ifq, int count)
pool->cache_count += filled;
}
+static struct io_zc_rx_buf *io_zc_get_buf_task_safe(struct io_zc_rx_ifq *ifq)
+{
+ struct io_zc_rx_pool *pool = ifq->pool;
+ struct io_zc_rx_buf *buf = NULL;
+ u32 pgid;
+
+ if (!READ_ONCE(pool->free_count))
+ return NULL;
+
+ spin_lock_bh(&pool->freelist_lock);
+ if (pool->free_count) {
+ pool->free_count--;
+ pgid = pool->freelist[pool->free_count];
+ buf = &pool->bufs[pgid];
+ atomic_set(&buf->refcount, 1);
+ }
+ spin_unlock_bh(&pool->freelist_lock);
+ return buf;
+}
+
struct io_zc_rx_buf *io_zc_rx_get_buf(struct io_zc_rx_ifq *ifq)
{
struct io_zc_rx_pool *pool = ifq->pool;
@@ -576,6 +596,11 @@ static struct io_zc_rx_ifq *io_zc_rx_ifq_skb(struct sk_buff *skb)
return NULL;
}
+static inline void io_zc_return_rbuf_cqe(struct io_zc_rx_ifq *ifq)
+{
+ ifq->cached_cq_tail--;
+}
+
static inline struct io_uring_rbuf_cqe *io_zc_get_rbuf_cqe(struct io_zc_rx_ifq *ifq)
{
struct io_uring_rbuf_cqe *cqe;
@@ -595,6 +620,51 @@ static inline struct io_uring_rbuf_cqe *io_zc_get_rbuf_cqe(struct io_zc_rx_ifq *
return cqe;
}
+static ssize_t zc_rx_copy_chunk(struct io_zc_rx_ifq *ifq, void *data,
+ unsigned int offset, size_t len)
+{
+ size_t copy_size, copied = 0;
+ struct io_uring_rbuf_cqe *cqe;
+ struct io_zc_rx_buf *buf;
+ unsigned int pgid;
+ int ret = 0, off = 0;
+ u8 *vaddr;
+
+ do {
+ cqe = io_zc_get_rbuf_cqe(ifq);
+ if (!cqe) {
+ ret = ENOBUFS;
+ break;
+ }
+ buf = io_zc_get_buf_task_safe(ifq);
+ if (!buf) {
+ io_zc_return_rbuf_cqe(ifq);
+ ret = -ENOMEM;
+ break;
+ }
+
+ vaddr = kmap_local_page(buf->page);
+ copy_size = min_t(size_t, PAGE_SIZE, len);
+ memcpy(vaddr, data + offset, copy_size);
+ kunmap_local(vaddr);
+
+ pgid = page_private(buf->page) & 0xffffffff;
+ io_zc_rx_get_buf_uref(ifq->pool, pgid);
+ io_zc_rx_put_buf(ifq, buf);
+
+ cqe->region = 0;
+ cqe->off = pgid * PAGE_SIZE + off;
+ cqe->len = copy_size;
+ cqe->flags = 0;
+
+ offset += copy_size;
+ len -= copy_size;
+ copied += copy_size;
+ } while (offset < len);
+
+ return copied ? copied : ret;
+}
+
static int zc_rx_recv_frag(struct io_zc_rx_ifq *ifq, const skb_frag_t *frag,
int off, int len, bool zc_skb)
{
@@ -618,9 +688,21 @@ static int zc_rx_recv_frag(struct io_zc_rx_ifq *ifq, const skb_frag_t *frag,
cqe->len = len;
cqe->flags = 0;
} else {
- /* TODO: copy frags that aren't backed by zc pages */
- WARN_ON_ONCE(1);
- return -ENOMEM;
+ u32 p_off, p_len, t, copied = 0;
+ u8 *vaddr;
+ int ret = 0;
+
+ skb_frag_foreach_page(frag, off, len,
+ page, p_off, p_len, t) {
+ vaddr = kmap_local_page(page);
+ ret = zc_rx_copy_chunk(ifq, vaddr, p_off, p_len);
+ kunmap_local(vaddr);
+
+ if (ret < 0)
+ return copied ? copied : ret;
+ copied += ret;
+ }
+ len = copied;
}
return len;
@@ -633,7 +715,7 @@ zc_rx_recv_skb(read_descriptor_t *desc, struct sk_buff *skb,
struct io_zc_rx_ifq *ifq = desc->arg.data;
struct io_zc_rx_ifq *skb_ifq;
struct sk_buff *frag_iter;
- unsigned start, start_off;
+ unsigned start, start_off = offset;
int i, copy, end, off;
bool zc_skb = true;
int ret = 0;
@@ -643,14 +725,27 @@ zc_rx_recv_skb(read_descriptor_t *desc, struct sk_buff *skb,
zc_skb = false;
if (WARN_ON_ONCE(skb_ifq))
return -EFAULT;
- pr_debug("non zerocopy pages are not supported\n");
- return -EFAULT;
}
- start = skb_headlen(skb);
- start_off = offset;
- // TODO: copy payload in skb linear data */
- WARN_ON_ONCE(offset < start);
+ if (unlikely(offset < skb_headlen(skb))) {
+ ssize_t copied;
+ size_t to_copy;
+
+ to_copy = min_t(size_t, skb_headlen(skb) - offset, len);
+ copied = zc_rx_copy_chunk(ifq, skb->data, offset, to_copy);
+ if (copied < 0) {
+ ret = copied;
+ goto out;
+ }
+ offset += copied;
+ len -= copied;
+ if (!len)
+ goto out;
+ if (offset != skb_headlen(skb))
+ goto out;
+ }
+
+ start = skb_headlen(skb);
for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
const skb_frag_t *frag;
--
2.39.3
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