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Subject: RE: [PATCH v8 00/18] Simplify running with high-numbered CPUs
Date: Mon, 6 Oct 2025 09:42:20 +0200
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From: =?iso-8859-1?Q?Morten_Br=F8rup?= <mb@smartsharesystems.com>
To: "Bruce Richardson" <bruce.richardson@intel.com>,
	<dev@dpdk.org>
Cc: <david.marchand@redhat.com>
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Bruce,

cpu_set_t is a fixed size array, with the size CPU_SETSIZE.
This is part of libc.

However, the kernel may be built with support for a different number of =
CPUs.
This means that e.g. sched_getaffinity() will fail with EINVAL if =
cpusetsize is smaller than the number of CPUs the kernel was built for.
For more information, refer to the description about "Dynamically sized =
CPU sets" here:
https://linux.die.net/man/3/cpu_alloc_size

With this series, consider ensuring that all DPDK functions taking a cpu =
set parameter also take a cpu set size parameter, to align with kernel =
APIs.
E.g.:
int sched_getaffinity(pid_t pid,
	size_t cpusetsize, cpu_set_t *mask), and
void CPU_ZERO_S(size_t setsize, cpu_set_t *set),
instead of:
void CPU_ZERO(cpu_set_t *set).

<feature creep>
Consider not using fixed size cpu sets (and CPU_SETSIZE) at all, but =
dynamically allocated cpu sets.
</feature creep>

<joke>
Consider not using fixed size lcore arrays (and RTE_MAX_LCORE) at all, =
but dynamically allocated lcore arrays.
</joke>


Venlig hilsen / Kind regards,
-Morten Br=F8rup