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When many packets reside on the same page, the bulking of page_ref modifications reduces the total number of atomic operations executed. Besides the necessary 2 operations on page alloc/free, we have the following extra ops per page: - one on WQE allocation (bump refcnt to maximum possible), - zero ops for SKBs, - one on WQE free, a constant of two operations in total, no matter how many packets/SKBs actually populate the page. Without this bulking, we have: - no ops on WQE allocation or free, - one op per SKB, Comparing the two methods when PAGE_SIZE is 4K: - As mentioned above, bulking method always executes 2 operations, not more, but not less. - In the default MTU configuration (1500, stride size is 2K), the non-bulking method execute 2 ops as well. - For larger MTUs with stride size of 4K, non-bulking method executes only a single op. - For XDP (stride size of 4K, no SKBs), non-bulking method executes no ops at all! Hence, to optimize the flows with linear SKB and XDP over Striding RQ, we here remove the page_ref bulking method. Performance testing: ConnectX-5, Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz. Single core packet rate (64 bytes). Early drop in TC: no degradation. XDP_DROP: before: 14,270,188 pps after: 20,503,603 pps, 43% improvement. Signed-off-by: Tariq Toukan <tariqt@mellanox.com> Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.