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Michal Schmidt
6cd695706f
On a kernel with preemption none or voluntary, 'ethtool -d' on a qede network device can cause a big latency spike. The biggest part of it is the loop in qed_grc_dump_ctx_data. The function is called only from the .get_size and .perform_dump callbacks for the "grc" feature defined in qed_features_lookup[]. As far as I can see, they are used in: - qed's devlink healh reporter .dump op - qede's ethtool get_regs/get_regs_len/get_dump_data ops - qedf's qedf_get_grc_dump, called from: - qedf_sysfs_write_grcdump - "grcdump" sysfs attribute write - qedf_wq_grcdump - a workqueue It is safe to sleep in all of them. Let's insert a cond_resched() in the outer loop to let other tasks run. Measured using this script: #!/bin/bash DEV=ens3f1 echo wakeup_rt > /sys/kernel/tracing/current_tracer echo 0 > /sys/kernel/tracing/tracing_max_latency echo 1 > /sys/kernel/tracing/tracing_on echo "Setting the task CPU affinity" taskset -p 1 $$ > /dev/null echo "Starting the real-time task" chrt -f 50 bash -c 'while sleep 0.01; do :; done' & sleep 1 echo "Running: ethtool -d $DEV" time ethtool -d $DEV > /dev/null kill %1 echo 0 > /sys/kernel/tracing/tracing_on echo "Measured latency: $(</sys/kernel/tracing/tracing_max_latency) us" echo "To see the latency trace: less /sys/kernel/tracing/trace" The patch lowers the latency from 180 ms to 53 ms on my test system with voluntary preemption. Signed-off-by: Michal Schmidt <mschmidt@redhat.com> Link: https://patch.msgid.link/20240930201307.330692-3-mschmidt@redhat.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.