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Message-ID: <20190724192253.00ac07bd@cakuba.netronome.com>
Date: Wed, 24 Jul 2019 19:22:53 -0700
From: Jakub Kicinski <jakub.kicinski@...ronome.com>
To: Kevin Laatz <kevin.laatz@...el.com>
Cc: netdev@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
bjorn.topel@...el.com, magnus.karlsson@...el.com,
jonathan.lemon@...il.com, saeedm@...lanox.com,
maximmi@...lanox.com, stephen@...workplumber.org,
bruce.richardson@...el.com, ciara.loftus@...el.com,
bpf@...r.kernel.org, intel-wired-lan@...ts.osuosl.org
Subject: Re: [PATCH bpf-next v3 03/11] xsk: add support to allow unaligned
chunk placement
On Wed, 24 Jul 2019 05:10:35 +0000, Kevin Laatz wrote:
> Currently, addresses are chunk size aligned. This means, we are very
> restricted in terms of where we can place chunk within the umem. For
> example, if we have a chunk size of 2k, then our chunks can only be placed
> at 0,2k,4k,6k,8k... and so on (ie. every 2k starting from 0).
>
> This patch introduces the ability to use unaligned chunks. With these
> changes, we are no longer bound to having to place chunks at a 2k (or
> whatever your chunk size is) interval. Since we are no longer dealing with
> aligned chunks, they can now cross page boundaries. Checks for page
> contiguity have been added in order to keep track of which pages are
> followed by a physically contiguous page.
>
> Signed-off-by: Kevin Laatz <kevin.laatz@...el.com>
> Signed-off-by: Ciara Loftus <ciara.loftus@...el.com>
> Signed-off-by: Bruce Richardson <bruce.richardson@...el.com>
>
> ---
> v2:
> - Add checks for the flags coming from userspace
> - Fix how we get chunk_size in xsk_diag.c
> - Add defines for masking the new descriptor format
> - Modified the rx functions to use new descriptor format
> - Modified the tx functions to use new descriptor format
>
> v3:
> - Add helper function to do address/offset masking/addition
> ---
> include/net/xdp_sock.h | 17 ++++++++
> include/uapi/linux/if_xdp.h | 9 ++++
> net/xdp/xdp_umem.c | 18 +++++---
> net/xdp/xsk.c | 86 ++++++++++++++++++++++++++++++-------
> net/xdp/xsk_diag.c | 2 +-
> net/xdp/xsk_queue.h | 68 +++++++++++++++++++++++++----
> 6 files changed, 170 insertions(+), 30 deletions(-)
>
> diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
> index 69796d264f06..738996c0f995 100644
> --- a/include/net/xdp_sock.h
> +++ b/include/net/xdp_sock.h
> @@ -19,6 +19,7 @@ struct xsk_queue;
> struct xdp_umem_page {
> void *addr;
> dma_addr_t dma;
> + bool next_pg_contig;
IIRC accesses to xdp_umem_page case a lot of cache misses, so having
this structure grow from 16 to 24B is a little unfortunate :(
Can we try to steal lower bits of addr or dma? Or perhaps not pre
compute this info at all?
> };
>
> struct xdp_umem_fq_reuse {
> @@ -48,6 +49,7 @@ struct xdp_umem {
> bool zc;
> spinlock_t xsk_list_lock;
> struct list_head xsk_list;
> + u32 flags;
> };
>
> struct xdp_sock {
> @@ -144,6 +146,15 @@ static inline void xsk_umem_fq_reuse(struct xdp_umem *umem, u64 addr)
>
> rq->handles[rq->length++] = addr;
> }
> +
> +static inline u64 xsk_umem_handle_offset(struct xdp_umem *umem, u64 handle,
> + u64 offset)
> +{
> + if (umem->flags & XDP_UMEM_UNALIGNED_CHUNKS)
> + return handle |= (offset << XSK_UNALIGNED_BUF_OFFSET_SHIFT);
> + else
> + return handle += offset;
> +}
> #else
> static inline int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
> {
> @@ -241,6 +252,12 @@ static inline void xsk_umem_fq_reuse(struct xdp_umem *umem, u64 addr)
> {
> }
>
> +static inline u64 xsk_umem_handle_offset(struct xdp_umem *umem, u64 handle,
> + u64 offset)
> +{
> + return NULL;
return 0?
> +}
> +
> #endif /* CONFIG_XDP_SOCKETS */
>
> #endif /* _LINUX_XDP_SOCK_H */
> diff --git a/include/uapi/linux/if_xdp.h b/include/uapi/linux/if_xdp.h
> index faaa5ca2a117..f8dc68fcdf78 100644
> --- a/include/uapi/linux/if_xdp.h
> +++ b/include/uapi/linux/if_xdp.h
> @@ -17,6 +17,9 @@
> #define XDP_COPY (1 << 1) /* Force copy-mode */
> #define XDP_ZEROCOPY (1 << 2) /* Force zero-copy mode */
>
> +/* Flags for xsk_umem_config flags */
> +#define XDP_UMEM_UNALIGNED_CHUNKS (1 << 0)
> +
> struct sockaddr_xdp {
> __u16 sxdp_family;
> __u16 sxdp_flags;
> @@ -53,6 +56,7 @@ struct xdp_umem_reg {
> __u64 len; /* Length of packet data area */
> __u32 chunk_size;
> __u32 headroom;
> + __u32 flags;
> };
>
> struct xdp_statistics {
> @@ -74,6 +78,11 @@ struct xdp_options {
> #define XDP_UMEM_PGOFF_FILL_RING 0x100000000ULL
> #define XDP_UMEM_PGOFF_COMPLETION_RING 0x180000000ULL
>
> +/* Masks for unaligned chunks mode */
> +#define XSK_UNALIGNED_BUF_OFFSET_SHIFT 48
> +#define XSK_UNALIGNED_BUF_ADDR_MASK \
> + ((1ULL << XSK_UNALIGNED_BUF_OFFSET_SHIFT) - 1)
> +
> /* Rx/Tx descriptor */
> struct xdp_desc {
> __u64 addr;
> diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
> index 83de74ca729a..952ca22103e9 100644
> --- a/net/xdp/xdp_umem.c
> +++ b/net/xdp/xdp_umem.c
> @@ -299,6 +299,7 @@ static int xdp_umem_account_pages(struct xdp_umem *umem)
>
> static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
> {
> + bool unaligned_chunks = mr->flags & XDP_UMEM_UNALIGNED_CHUNKS;
> u32 chunk_size = mr->chunk_size, headroom = mr->headroom;
> unsigned int chunks, chunks_per_page;
> u64 addr = mr->addr, size = mr->len;
> @@ -314,7 +315,10 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
> return -EINVAL;
> }
>
> - if (!is_power_of_2(chunk_size))
> + if (mr->flags & ~(XDP_UMEM_UNALIGNED_CHUNKS))
parens unnecessary, consider adding a define for known flags.
> + return -EINVAL;
> +
> + if (!unaligned_chunks && !is_power_of_2(chunk_size))
> return -EINVAL;
>
> if (!PAGE_ALIGNED(addr)) {
> @@ -331,9 +335,11 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
> if (chunks == 0)
> return -EINVAL;
>
> - chunks_per_page = PAGE_SIZE / chunk_size;
> - if (chunks < chunks_per_page || chunks % chunks_per_page)
> - return -EINVAL;
> + if (!unaligned_chunks) {
> + chunks_per_page = PAGE_SIZE / chunk_size;
> + if (chunks < chunks_per_page || chunks % chunks_per_page)
> + return -EINVAL;
> + }
>
> headroom = ALIGN(headroom, 64);
>
> @@ -342,13 +348,15 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
> return -EINVAL;
>
> umem->address = (unsigned long)addr;
> - umem->chunk_mask = ~((u64)chunk_size - 1);
> + umem->chunk_mask = unaligned_chunks ? XSK_UNALIGNED_BUF_ADDR_MASK
> + : ~((u64)chunk_size - 1);
> umem->size = size;
> umem->headroom = headroom;
> umem->chunk_size_nohr = chunk_size - headroom;
> umem->npgs = size / PAGE_SIZE;
> umem->pgs = NULL;
> umem->user = NULL;
> + umem->flags = mr->flags;
> INIT_LIST_HEAD(&umem->xsk_list);
> spin_lock_init(&umem->xsk_list_lock);
>
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 59b57d708697..b3ab653091c4 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -45,7 +45,7 @@ EXPORT_SYMBOL(xsk_umem_has_addrs);
>
> u64 *xsk_umem_peek_addr(struct xdp_umem *umem, u64 *addr)
> {
> - return xskq_peek_addr(umem->fq, addr);
> + return xskq_peek_addr(umem->fq, addr, umem);
> }
> EXPORT_SYMBOL(xsk_umem_peek_addr);
>
> @@ -55,21 +55,42 @@ void xsk_umem_discard_addr(struct xdp_umem *umem)
> }
> EXPORT_SYMBOL(xsk_umem_discard_addr);
>
> +/* If a buffer crosses a page boundary, we need to do 2 memcpy's, one for
> + * each page. This is only required in copy mode.
> + */
> +static void __xsk_rcv_memcpy(struct xdp_umem *umem, u64 addr, void *from_buf,
> + u32 len, u32 metalen)
> +{
> + void *to_buf = xdp_umem_get_data(umem, addr);
> +
> + if (xskq_crosses_non_contig_pg(umem, addr, len + metalen)) {
> + void *next_pg_addr = umem->pages[(addr >> PAGE_SHIFT) + 1].addr;
> + u64 page_start = addr & (PAGE_SIZE - 1);
> + u64 first_len = PAGE_SIZE - (addr - page_start);
> +
> + memcpy(to_buf, from_buf, first_len + metalen);
> + memcpy(next_pg_addr, from_buf + first_len, len - first_len);
> +
> + return;
> + }
> +
> + memcpy(to_buf, from_buf, len + metalen);
> +}
Why handle this case gracefully? Real XSK use is the zero copy mode,
having extra code to make copy mode more permissive seems a little
counter productive IMHO.
> static int __xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
> {
> - void *to_buf, *from_buf;
> + u64 offset = xs->umem->headroom;
> + void *from_buf;
> u32 metalen;
> u64 addr;
> int err;
>
> - if (!xskq_peek_addr(xs->umem->fq, &addr) ||
> + if (!xskq_peek_addr(xs->umem->fq, &addr, xs->umem) ||
> len > xs->umem->chunk_size_nohr - XDP_PACKET_HEADROOM) {
> xs->rx_dropped++;
> return -ENOSPC;
> }
>
> - addr += xs->umem->headroom;
> -
> if (unlikely(xdp_data_meta_unsupported(xdp))) {
> from_buf = xdp->data;
> metalen = 0;
> @@ -78,9 +99,13 @@ static int __xsk_rcv(struct xdp_sock *xs, struct xdp_buff *xdp, u32 len)
> metalen = xdp->data - xdp->data_meta;
> }
>
> - to_buf = xdp_umem_get_data(xs->umem, addr);
> - memcpy(to_buf, from_buf, len + metalen);
> - addr += metalen;
> + __xsk_rcv_memcpy(xs->umem, addr + offset, from_buf, len, metalen);
> +
> + offset += metalen;
> + if (xs->umem->flags & XDP_UMEM_UNALIGNED_CHUNKS)
> + addr |= offset << XSK_UNALIGNED_BUF_OFFSET_SHIFT;
> + else
> + addr += offset;
> err = xskq_produce_batch_desc(xs->rx, addr, len);
> if (!err) {
> xskq_discard_addr(xs->umem->fq);
> @@ -127,6 +152,7 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp)
> u32 len = xdp->data_end - xdp->data;
> void *buffer;
> u64 addr;
> + u64 offset = xs->umem->headroom;
reverse xmas tree, please
> int err;
>
> spin_lock_bh(&xs->rx_lock);
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