91bfe210e1
Souradeep investigated that the driver performs faster if IRQs are spread on CPUs with the following heuristics: 1. No more than one IRQ per CPU, if possible; 2. NUMA locality is the second priority; 3. Sibling dislocality is the last priority. Let's consider this topology: Node 0 1 Core 0 1 2 3 CPU 0 1 2 3 4 5 6 7 The most performant IRQ distribution based on the above topology and heuristics may look like this: IRQ Nodes Cores CPUs 0 1 0 0-1 1 1 1 2-3 2 1 0 0-1 3 1 1 2-3 4 2 2 4-5 5 2 3 6-7 6 2 2 4-5 7 2 3 6-7 The irq_setup() routine introduced in this patch leverages the for_each_numa_hop_mask() iterator and assigns IRQs to sibling groups as described above. According to [1], for NUMA-aware but sibling-ignorant IRQ distribution based on cpumask_local_spread() performance test results look like this: ./ntttcp -r -m 16 NTTTCP for Linux 1.4.0 --------------------------------------------------------- 08:05:20 INFO: 17 threads created 08:05:28 INFO: Network activity progressing... 08:06:28 INFO: Test run completed. 08:06:28 INFO: Test cycle finished. 08:06:28 INFO: ##### Totals: ##### 08:06:28 INFO: test duration :60.00 seconds 08:06:28 INFO: total bytes :630292053310 08:06:28 INFO: throughput :84.04Gbps 08:06:28 INFO: retrans segs :4 08:06:28 INFO: cpu cores :192 08:06:28 INFO: cpu speed :3799.725MHz 08:06:28 INFO: user :0.05% 08:06:28 INFO: system :1.60% 08:06:28 INFO: idle :96.41% 08:06:28 INFO: iowait :0.00% 08:06:28 INFO: softirq :1.94% 08:06:28 INFO: cycles/byte :2.50 08:06:28 INFO: cpu busy (all) :534.41% For NUMA- and sibling-aware IRQ distribution, the same test works 15% faster: ./ntttcp -r -m 16 NTTTCP for Linux 1.4.0 --------------------------------------------------------- 08:08:51 INFO: 17 threads created 08:08:56 INFO: Network activity progressing... 08:09:56 INFO: Test run completed. 08:09:56 INFO: Test cycle finished. 08:09:56 INFO: ##### Totals: ##### 08:09:56 INFO: test duration :60.00 seconds 08:09:56 INFO: total bytes :741966608384 08:09:56 INFO: throughput :98.93Gbps 08:09:56 INFO: retrans segs :6 08:09:56 INFO: cpu cores :192 08:09:56 INFO: cpu speed :3799.791MHz 08:09:56 INFO: user :0.06% 08:09:56 INFO: system :1.81% 08:09:56 INFO: idle :96.18% 08:09:56 INFO: iowait :0.00% 08:09:56 INFO: softirq :1.95% 08:09:56 INFO: cycles/byte :2.25 08:09:56 INFO: cpu busy (all) :569.22% [1] https://lore.kernel.org/all/20231211063726.GA4977@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net/ Signed-off-by: Yury Norov <yury.norov@gmail.com> Co-developed-by: Souradeep Chakrabarti <schakrabarti@linux.microsoft.com> Signed-off-by: Paolo Abeni <pabeni@redhat.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.