Fork of alistair23 Linux kernel for reMarkable from https://github.com/alistair23/linux
60bbf7eeef
This patch shows how it is possible to have both the driver local page cache, which uses elevated refcnt for "catching"/avoiding SKB put_page returns the page through the page allocator. And at the same time, have pages getting returned to the page_pool from ndp_xdp_xmit DMA completion. The performance improvement for XDP_REDIRECT in this patch is really good. Especially considering that (currently) the xdp_return_frame API and page_pool_put_page() does per frame operations of both rhashtable ID-lookup and locked return into (page_pool) ptr_ring. (It is the plan to remove these per frame operation in a followup patchset). The benchmark performed was RX on mlx5 and XDP_REDIRECT out ixgbe, with xdp_redirect_map (using devmap) . And the target/maximum capability of ixgbe is 13Mpps (on this HW setup). Before this patch for mlx5, XDP redirected frames were returned via the page allocator. The single flow performance was 6Mpps, and if I started two flows the collective performance drop to 4Mpps, because we hit the page allocator lock (further negative scaling occurs). Two test scenarios need to be covered, for xdp_return_frame API, which is DMA-TX completion running on same-CPU or cross-CPU free/return. Results were same-CPU=10Mpps, and cross-CPU=12Mpps. This is very close to our 13Mpps max target. The reason max target isn't reached in cross-CPU test, is likely due to RX-ring DMA unmap/map overhead (which doesn't occur in ixgbe to ixgbe testing). It is also planned to remove this unnecessary DMA unmap in a later patchset V2: Adjustments requested by Tariq - Changed page_pool_create return codes not return NULL, only ERR_PTR, as this simplifies err handling in drivers. - Save a branch in mlx5e_page_release - Correct page_pool size calc for MLX5_WQ_TYPE_LINKED_LIST_STRIDING_RQ V5: Updated patch desc V8: Adjust for |
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README
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.