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6f57428460
Start using the page_pool skb recycling api to recycle all pages back to the page pool and stop using atomic page reference counting. The mlx5e driver used to manage in-flight pages using page refcounting: for each fragment there were 2 atomic write operations happening (one for building the skb and one on skb release). The page_pool api introduced a method to track page fragments more optimally: * The page's pp_fragment_count is set to a large bias on page alloc (1 x atomic write operation). * The driver tracks the actual page fragments in a non atomic variable. * When the skb is recycled, pp_fragment_count is decremented (atomic write operation). * When page is released in the driver, the unused number of fragments (relative to the bias) is deducted from pp_fragment_count (atomic write operation). * Last page defragmentation will only be an atomic read. So in total there are `number of fragments + 1` atomic write ops. As opposed to previously: `2 * frags` atomic writes ops. Pages are wrapped in a mlx5e_frag_page structure which also contains the number of fragments. This makes it easy to count the fragments in the driver. This change brings performance improvements for the case when the old rx page_cache had low recycling rates due to head of queue blocking. For a iperf3 TCP test with a single stream, on a single core (iperf and receive queue running on same core), the following improvements can be noticed: * Striding rq: - before (net-next baseline): bitrate = 30.1 Gbits/sec - after : bitrate = 31.4 Gbits/sec (diff: 4.14 %) * Legacy rq: - before (net-next baseline): bitrate = 30.2 Gbits/sec - after : bitrate = 33.0 Gbits/sec (diff: 8.48 %) There are 2 temporary performance degradations introduced: 1) TCP streams that had a good recycling rate with the old page_cache have a degradation for both striding and linear rq. This is due to very low page pool cache recycling: the pages are released during skb recycle which will release pages to the page pool ring for safety. The following patches in this series will tackle this problem by deferring the page release in the driver to increase the chance of having pages recycled to the cache. 2) XDP performance is now lower (4-5 %) due to the higher number of atomic operations used for fragment management. But this opens the door for supporting multiple packets per page in XDP, which will bring a big gain. Otherwise, performance is similar to baseline. Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com> Reviewed-by: Tariq Toukan <tariqt@nvidia.com> Signed-off-by: Saeed Mahameed <saeedm@nvidia.com> |
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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.
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.