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Currently, the mlx5_eq_comp_int() interrupt handler schedules a tasklet to call mlx5_cq_tasklet_cb() if it processes any completions. For CQs whose completions don't need to be processed in tasklet context, this adds unnecessary overhead. In a heavy TCP workload, we see 4% of CPU time spent on the tasklet_trylock() in tasklet_action_common(), with a smaller amount spent on the atomic operations in tasklet_schedule(), tasklet_clear_sched(), and locking the spinlock in mlx5_cq_tasklet_cb(). TCP completions are handled by mlx5e_completion_event(), which schedules NAPI to poll the queue, so they don't need tasklet processing. Schedule the tasklet in mlx5_add_cq_to_tasklet() instead to avoid this overhead. mlx5_add_cq_to_tasklet() is responsible for enqueuing the CQs to be processed in tasklet context, so it can schedule the tasklet. CQs that need tasklet processing have their interrupt comp handler set to mlx5_add_cq_to_tasklet(), so they will schedule the tasklet. CQs that don't need tasklet processing won't schedule the tasklet. To avoid scheduling the tasklet multiple times during the same interrupt, only schedule the tasklet in mlx5_add_cq_to_tasklet() if the tasklet work queue was empty before the new CQ was pushed to it. The additional branch in mlx5_add_cq_to_tasklet(), called for each EQE, may add a small cost for the userspace Infiniband CQs whose completions are processed in tasklet context. But this seems worth it to avoid the tasklet overhead for CQs that don't need it. Note that the mlx4 driver works the same way: it schedules the tasklet in mlx4_add_cq_to_tasklet() and only if the work queue was empty before. Signed-off-by: Caleb Sander Mateos <csander@purestorage.com> Reviewed-by: Parav Pandit <parav@nvidia.com> Acked-by: Tariq Toukan <tariqt@nvidia.com> Acked-by: Saeed Mahameed <saeedm@nvidia.com> Link: https://patch.msgid.link/20241105204000.1807095-1-csander@purestorage.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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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 reStructuredText 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.