Re: [Intel-wired-lan] [PATCH v2 00/10] XDP unaligned chunk placement support

[Magnus Karlsson <magnus.karlsson@gmail.com>]

On Tue, Jul 23, 2019 at 11:08 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> Johnathan, Bjorn, Jakub,
> Please review!
> The patch set has been pending for a week.

There is a v3 coming out shortly so I suggest we wait for that. It
will have Mellanox support for this feature too and some clean ups. I
refrained from posting a review on the mailing list due to the merge
window being closed last week, but maybe that was not correct. Should
I still post reviews for new features submitted during the closed
merge window period? I am happy to do it since I do not have any other
tasks during that time. It is a quite period for me. Just let me know.

/Magnus

> On Tue, Jul 16, 2019 at 4:21 AM Kevin Laatz <kevin.laatz@intel.com> wrote:
> >
> > This patch set adds the ability to use unaligned chunks in the XDP umem.
> >
> > Currently, all chunk addresses passed to the umem are masked to be chunk
> > size aligned (default is 2k, max is PAGE_SIZE). This limits where we can
> > place chunks within the umem as well as limiting the packet sizes that are
> > supported.
> >
> > The changes in this patch set removes these restrictions, allowing XDP to
> > be more flexible in where it can place a chunk within a umem. By relaxing
> > where the chunks can be placed, it allows us to use an arbitrary buffer
> > size and place that wherever we have a free address in the umem. These
> > changes add the ability to support arbitrary frame sizes up to 4k
> > (PAGE_SIZE) and make it easy to integrate with other existing frameworks
> > that have their own memory management systems, such as DPDK.
> >
> > Since we are now dealing with arbitrary frame sizes, we need also need to
> > update how we pass around addresses. Currently, the addresses can simply be
> > masked to 2k to get back to the original address. This becomes less trivial
> > when using frame sizes that are not a 'power of 2' size. This patch set
> > modifies the Rx/Tx descriptor format to use the upper 16-bits of the addr
> > field for an offset value, leaving the lower 48-bits for the address (this
> > leaves us with 256 Terabytes, which should be enough!). We only need to use
> > the upper 16-bits to store the offset when running in unaligned mode.
> > Rather than adding the offset (headroom etc) to the address, we will store
> > it in the upper 16-bits of the address field. This way, we can easily add
> > the offset to the address where we need it, using some bit manipulation and
> > addition, and we can also easily get the original address wherever we need
> > it (for example in i40e_zca_free) by simply masking to get the lower
> > 48-bits of the address field.
> >
> > The numbers below were recorded with the following set up:
> >   - Intel(R) Xeon(R) Gold 6140 CPU @ 2.30GHz
> >   - Intel Corporation Ethernet Controller XXV710 for 25GbE SFP28 (rev 02)
> >   - Driver: i40e
> >   - Application: xdpsock with l2fwd (single interface)
> >
> > These are solely for comparing performance with and without the patches.
> > The largest drop was ~1% (in zero-copy mode).
> >
> > +-------------------------+------------+-----------------+-------------+
> > | Buffer size: 2048       | SKB mode   | Zero-copy       | Copy        |
> > +-------------------------+------------+-----------------+-------------+
> > | Aligned (baseline)      | 1.7 Mpps   | 15.3 Mpps       | 2.08 Mpps   |
> > +-------------------------+------------+-----------------+-------------+
> > | Aligned (with patches)  | 1.7 Mpps   | 15.1 Mpps       | 2.08 Mpps   |
> > +-------------------------+------------+-----------------+-------------+
> > | Unaligned               | 1.7 Mpps   | 14.5 Mpps       | 2.08 Mpps   |
> > +-------------------------+------------+-----------------+-------------+
> >
> > NOTE: We are currently working on the changes required in the Mellanox
> > driver. We will include these in the v3.
> >
> > Structure of the patchset:
> > Patch 1:
> >   - Remove unnecessary masking and headroom addition during zero-copy Rx
> >     buffer recycling in i40e. This change is required in order for the
> >     buffer recycling to work in the unaligned chunk mode.
> >
> > Patch 2:
> >   - Remove unnecessary masking and headroom addition during
> >     zero-copy Rx buffer recycling in ixgbe. This change is required in
> >     order for the  buffer recycling to work in the unaligned chunk mode.
> >
> > Patch 3:
> >   - Add infrastructure for unaligned chunks. Since we are dealing with
> >     unaligned chunks that could potentially cross a physical page boundary,
> >     we add checks to keep track of that information. We can later use this
> >     information to correctly handle buffers that are placed at an address
> >     where they cross a page boundary.  This patch also modifies the
> >     existing Rx and Tx functions to use the new descriptor format. To
> >     handle addresses correctly, we need to mask appropriately based on
> >     whether we are in aligned or unaligned mode.
> >
> > Patch 4:
> >   - This patch updates the i40e driver to make use of the new descriptor
> >     format. The new format is particularly useful here since we can now
> >     retrieve the original address in places like i40e_zca_free with ease.
> >     This saves us doing various calculations to get the original address
> >     back.
> >
> > Patch 5:
> >   - This patch updates the ixgbe driver to make use of the new descriptor
> >     format. The new format is particularly useful here since we can now
> >     retrieve the original address in places like ixgbe_zca_free with ease.
> >     This saves us doing various calculations to get the original address
> >     back.
> >
> > Patch 6:
> >   - Add flags for umem configuration to libbpf
> >
> > Patch 7:
> >   - Modify xdpsock application to add a command line option for
> >     unaligned chunks
> >
> > Patch 8:
> >   - Since we can now run the application in unaligned chunk mode, we need
> >     to make sure we recycle the buffers appropriately.
> >
> > Patch 9:
> >   - Adds hugepage support to the xdpsock application
> >
> > Patch 10:
> >   - Documentation update to include the unaligned chunk scenario. We need
> >     to explicitly state that the incoming addresses are only masked in the
> >     aligned chunk mode and not the unaligned chunk mode.
> >
> > ---
> > v2:
> >   - fixed checkpatch issues
> >   - fixed Rx buffer recycling for unaligned chunks in xdpsock
> >   - removed unused defines
> >   - fixed how chunk_size is calculated in xsk_diag.c
> >   - added some performance numbers to cover letter
> >   - modified descriptor format to make it easier to retrieve original
> >     address
> >   - removed patch adding off_t off to the zero copy allocator. This is no
> >     longer needed with the new descriptor format.
> >
> > Kevin Laatz (10):
> >   i40e: simplify Rx buffer recycle
> >   ixgbe: simplify Rx buffer recycle
> >   xsk: add support to allow unaligned chunk placement
> >   i40e: modify driver for handling offsets
> >   ixgbe: modify driver for handling offsets
> >   libbpf: add flags to umem config
> >   samples/bpf: add unaligned chunks mode support to xdpsock
> >   samples/bpf: add buffer recycling for unaligned chunks to xdpsock
> >   samples/bpf: use hugepages in xdpsock app
> >   doc/af_xdp: include unaligned chunk case
> >
> >  Documentation/networking/af_xdp.rst          | 10 ++-
> >  drivers/net/ethernet/intel/i40e/i40e_xsk.c   | 39 +++++----
> >  drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c | 39 +++++----
> >  include/net/xdp_sock.h                       |  2 +
> >  include/uapi/linux/if_xdp.h                  |  9 ++
> >  net/xdp/xdp_umem.c                           | 17 ++--
> >  net/xdp/xsk.c                                | 89 ++++++++++++++++----
> >  net/xdp/xsk_diag.c                           |  2 +-
> >  net/xdp/xsk_queue.h                          | 70 +++++++++++++--
> >  samples/bpf/xdpsock_user.c                   | 61 ++++++++++----
> >  tools/include/uapi/linux/if_xdp.h            |  4 +
> >  tools/lib/bpf/xsk.c                          |  3 +
> >  tools/lib/bpf/xsk.h                          |  2 +
> >  13 files changed, 266 insertions(+), 81 deletions(-)
> >
> > --
> > 2.17.1
> >
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