netdev - Re: [PATCH bpf-next v5 0/4] xsk: Support UMEM chunk_size > PAGE

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Date:   Wed, 12 Apr 2023 15:43:31 +0200
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     Kal Conley <kal.conley@...tris.com>
Cc:     Magnus Karlsson <magnus.karlsson@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 0/4] xsk: Support UMEM chunk_size > PAGE_SIZE

On Mon, 10 Apr 2023 at 14:08, Kal Conley <kal.conley@...tris.com> wrote:
>
> The main purpose of this patchset is to add AF_XDP support for UMEM
> chunk sizes > PAGE_SIZE. This is enabled for UMEMs backed by HugeTLB
> pages.
>
> Note, v5 fixes a major bug in previous versions of this patchset.
> In particular, dma_map_page_attrs used to be called once for each
> order-0 page in a hugepage with the assumption that returned I/O
> addresses are contiguous within a hugepage. This assumption is incorrect
> when an IOMMU is enabled. To fix this, v5 does DMA page accounting
> accounting at hugepage granularity.

Thank you so much Kal for implementing this feature. After you have
fixed the three small things I had for patch #2, you have my ack for
the whole set below. Please add it.

For the whole set:
Acked-by: Magnus Karlsson <magnus.karlsson@...el.com>

It would be great if you have the time and desire to also take this to
zero-copy mode. I have had multiple AF_XDP users mailing me privately
that such a feature would be very useful for them. For some of them it
was even a requirement to be able to get down to the latencies they
were aiming for.

> Changes since v4:
>   * Use hugepages in DMA map (fixes zero-copy mode with IOMMU).
>   * Use pool->dma_pages to check for DMA. This change is needed to avoid
>     performance regressions).
>   * Update commit message and benchmark table.
>
> Changes since v3:
>   * Fix checkpatch.pl whitespace error.
>
> Changes since v2:
>   * Related fixes/improvements included with v2 have been removed. These
>     changes have all been resubmitted as standalone patchsets.
>   * Minimize uses of #ifdef CONFIG_HUGETLB_PAGE.
>   * Improve AF_XDP documentation.
>   * Update benchmark table in commit message.
>
> Changes since v1:
>   * Add many fixes/improvements to the XSK selftests.
>   * Add check for unaligned descriptors that overrun UMEM.
>   * Fix compile errors when CONFIG_HUGETLB_PAGE is not set.
>   * Fix incorrect use of _Static_assert.
>   * Update AF_XDP documentation.
>   * Rename unaligned 9K frame size test.
>   * Make xp_check_dma_contiguity less conservative.
>   * Add more information to benchmark table.
>
> Thanks to Magnus Karlsson for all his support!
>
> Happy Easter!
>
> Kal Conley (4):
>   xsk: Use pool->dma_pages to check for DMA
>   xsk: Support UMEM chunk_size > PAGE_SIZE
>   selftests: xsk: Use hugepages when umem->frame_size > PAGE_SIZE
>   selftests: xsk: Add tests for 8K and 9K frame sizes
>
>  Documentation/networking/af_xdp.rst      | 36 ++++++++++------
>  include/net/xdp_sock.h                   |  2 +
>  include/net/xdp_sock_drv.h               | 12 ++++++
>  include/net/xsk_buff_pool.h              | 12 +++---
>  net/xdp/xdp_umem.c                       | 55 +++++++++++++++++++-----
>  net/xdp/xsk_buff_pool.c                  | 43 ++++++++++--------
>  tools/testing/selftests/bpf/xskxceiver.c | 27 +++++++++++-
>  tools/testing/selftests/bpf/xskxceiver.h |  2 +
>  8 files changed, 142 insertions(+), 47 deletions(-)
>
> --
> 2.39.2
>