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1fbf1252df
mlx5_eq_cq_get() is called in IRQ handler, the spinlock inside gets a lot of contentions when we test some heavy workload with 60 RX queues and 80 CPU's, and it is clearly shown in the flame graph. In fact, radix_tree_lookup() is perfectly fine with RCU read lock, we don't have to take a spinlock on this hot path. This is pretty much similar to commit291c566a28("net/mlx4_core: Fix racy CQ (Completion Queue) free"). Slow paths are still serialized with the spinlock, and with synchronize_irq() it should be safe to just move the fast path to RCU read lock. This patch itself reduces the latency by about 50% for our memcached workload on a 4.14 kernel we test. In upstream, as pointed out by Saeed, this spinlock gets some rework in commit02d92f7903("net/mlx5: CQ Database per EQ"), so the difference could be smaller. Cc: Saeed Mahameed <saeedm@mellanox.com> Cc: Tariq Toukan <tariqt@mellanox.com> Acked-by: Saeed Mahameed <saeedm@mellanox.com> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
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.