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For simplicity reasons, the driver avoids crossing work queue fragment boundaries within the same TX WQE (Work-Queue Element). Until today, as the number of packets in a TX MPWQE (Multi-Packet WQE) descriptor is not known in advance, the driver pre-prepared contiguous memory for the largest possible WQE. For this, when getting too close to the fragment edge, having no room for the largest WQE possible, the driver was filling the fragment remainder with NOP descriptors, aligning the next descriptor to the beginning of the next fragment. Generating and handling these NOPs wastes resources, like: CPU cycles, work-queue entries fetched to the device, and PCI bandwidth. In this patch, we replace this NOPs filling mechanism in the TX MPWQE flow. Instead, we utilize the remaining entries of the fragment with a TX MPWQE. If this room turns out to be too small, we simply open an additional descriptor starting at the beginning of the next fragment. Performance benchmark: uperf test, single server against 3 clients. TCP multi-stream, bidir, traffic profile "2x350B read, 1400B write". Bottleneck is in inbound PCI bandwidth (device POV). +---------------+------------+------------+--------+ | | Before | After | | +---------------+------------+------------+--------+ | BW | 117.4 Gbps | 121.1 Gbps | +3.1% | +---------------+------------+------------+--------+ | tx_packets | 15 M/sec | 15.5 M/sec | +3.3% | +---------------+------------+------------+--------+ | tx_nops | 3 M/sec | 0 | -100% | +---------------+------------+------------+--------+ Signed-off-by: Tariq Toukan <tariqt@nvidia.com> Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com> Reviewed-by: Simon Horman <horms@kernel.org> Link: https://patch.msgid.link/1742391746-118647-1-git-send-email-tariqt@nvidia.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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.