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elf: Add CPU iteration support for future use in ld.so diagnostics

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Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
This commit is contained in:
Florian Weimer 2024-04-08 16:48:55 +02:00
parent 1f94147a79
commit 5653ccd847
3 changed files with 236 additions and 0 deletions
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136
elf/dl-iterate_cpu.h Normal file
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/* Iterate over all CPUs, for CPU-specific diagnostics.
Copyright (C) 2024 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#ifndef DL_ITERATE_CPU_H
#define DL_ITERATE_CPU_H
#include <dl-affinity.h>
#include <stdbool.h>
struct dl_iterate_cpu
{
/* Sequential iteration count, starting at 0. */
unsigned int processor_index;
/* Requested CPU. Can be -1 if affinity could not be set. */
int requested_cpu;
/* Observed current CPU. -1 if unavailable. */
int actual_cpu;
/* Observed node ID for the CPU. -1 if unavailable. */
int actual_node;
/* Internal fields to implement the iteration. */
/* Affinity as obtained by _dl_iterate_cpu_init, using
_dl_getaffinity. Space for 8,192 CPUs. */
unsigned long int mask_reference[8192 / sizeof (unsigned long int) / 8];
/* This array is used by _dl_setaffinity calls. */
unsigned long int mask_request[8192 / sizeof (unsigned long int) / 8];
/* Return value from the initial _dl_getaffinity call. */
int length_reference;
};
static void
_dl_iterate_cpu_init (struct dl_iterate_cpu *dic)
{
dic->length_reference
= _dl_getaffinity (dic->mask_reference, sizeof (dic->mask_reference));
/* Prepare for the first _dl_iterate_cpu_next call. */
dic->processor_index = -1;
dic->requested_cpu = -1;
}
static bool
_dl_iterate_cpu_next (struct dl_iterate_cpu *dic)
{
++dic->processor_index;
if (dic->length_reference > 0)
{
/* Search for the next CPU to switch to. */
while (true)
{
++dic->requested_cpu;
/* Array index and bit number within the array. */
unsigned int long_index
= dic->requested_cpu / sizeof (unsigned long int) / 8;
unsigned int bit_index
= dic->requested_cpu % (sizeof (unsigned long int) * 8);
if (long_index * sizeof (unsigned long int) >= dic->length_reference)
/* All possible CPUs have been covered. */
return false;
unsigned long int bit = 1UL << bit_index;
if (dic->mask_reference[long_index] & bit)
{
/* The CPU is available. Try to select it. */
dic->mask_request[long_index] = bit;
if (_dl_setaffinity (dic->mask_request,
(long_index + 1)
* sizeof (unsigned long int)) < 0)
{
/* Record that we could not perform a CPU request. */
dic->length_reference = -1;
if (dic->processor_index > 0)
/* We already reported something. There is no need to
continue because the new data is probably not useful. */
return false;
}
/* Clear the bit in case the next iteration switches to the
next long value. */
dic->mask_request[long_index] = 0;
/* We found a CPU to run on. */
break;
}
}
}
else
{
/* No way to set CPU affinity. Iterate just once. */
if (dic->processor_index > 0)
return false;
}
/* Fill in the actual CPU information. CPU pinning may not actually
be effective, depending on the container host. */
unsigned int cpu, node;
if (_dl_getcpu (&cpu, &node) < 0)
{
/* No CPU information available. */
dic->actual_cpu = -1;
dic->actual_node = -1;
}
else
{
dic->actual_cpu = cpu;
dic->actual_node = node;
}
return true;
}
#endif /* DL_ITERATE_CPU_H */

54
sysdeps/generic/dl-affinity.h Normal file
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/* CPU affinity handling for the dynamic linker. Stub version.
Copyright (C) 2024 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#ifndef DL_AFFINITY_H
#define DL_AFFINITY_H
#include <errno.h>
#include <stddef.h>
/* On success, write the current CPU ID to *CPU, and the current node
ID to *NODE, and return 0. Return a negative error code on
failure. */
static inline int
_dl_getcpu (unsigned int *cpu, unsigned int *node)
{
return -ENOSYS;
}
/* On success, write CPU ID affinity bits for the current thread to
*BITS, which must be SIZE bytes long, and return the number of
bytes updated, a multiple of sizeof (unsigned long int). On
failure, return a negative error code. */
static int
_dl_getaffinity (unsigned long int *bits, size_t size)
{
return -ENOSYS;
}
/* Set the CPU affinity mask for the current thread to *BITS, using
the SIZE bytes from that array, which should be a multiple of
sizeof (unsigned long int). Return 0 on success, and a negative
error code on failure. */
static int
_dl_setaffinity (const unsigned long int *bits, size_t size)
{
return -ENOSYS;
}
#endif /* DL_AFFINITY_H */

46
sysdeps/unix/sysv/linux/dl-affinity.h Normal file
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/* CPU affinity handling for the dynamic linker. Linux version.
Copyright (C) 2024 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
/* See sysdeps/generic/dl-affinity.h for documentation of these interfaces. */
#ifndef DL_AFFINITY_H
#define DL_AFFINITY_H
#include <sysdep.h>
#include <stddef.h>
#include <unistd.h>
static inline int
_dl_getcpu (unsigned int *cpu, unsigned int *node)
{
return INTERNAL_SYSCALL_CALL (getcpu, cpu, node);
}
static int
_dl_getaffinity (unsigned long int *bits, size_t size)
{
return INTERNAL_SYSCALL_CALL (sched_getaffinity, /* TID */ 0, size, bits);
}
static int
_dl_setaffinity (const unsigned long int *bits, size_t size)
{
return INTERNAL_SYSCALL_CALL (sched_setaffinity, /* TID */ 0, size, bits);
}
#endif /* DL_AFFINITY_H */