cpuinfo

The cpuinfo area contains information about each CPU in the system, such as the CPU type, speed, capabilities, performance, and cache sizes.

The number of cpuinfo_entry instances is equal to the value in the num_cpu member of the syspage_entry structure.

Each cpuinfo_entry structure is automatically filled in by the startup library function init_cpuinfo(). The members include:

cpu: A number that represents the type of CPU. The meaning of this number depends on the CPU architecture. For example, for the x86 processor family, this number is the processor chip number (e.g., 586).
speed: The MHz rating of the processor.
flags: The CPU capabilities; see “flags” below.
smp_hwcoreid: A number identifying each core; used for SMP.
idle_history: Reserved.
spare1: Not used.
name: An index into the strings member in the system page structure. The character string at the specified index contains an ASCII, NULL-terminated machine name.
ins_cache: An index into the cacheattr array, which is described below. This index points to the first definition in a list for the instruction cache.
data_cache: An index into the cacheattr array, which is described below. This index points to the first definition in a list for the data cache.

`flags`

The flags member contains a bitmapped indication of the CPU's capabilities. The prefix for a flag name (i.e., macro constant) indicates the CPU family it applies to (e.g., ARM_ indicates that this constant is for use on the ARM family of processors). If there is no prefix, the constant is generic; it is relevant to any CPU supported by QNX Neutrino RTOS.

Generic flags are defined in <sys/syspage.h>, while architecture-specific flags are defined in <arch/syspage.h>. You'll need the values to interpret the output of the pidin syspage command.

The bits include the following:

This bit:	Means that the CPU has or supports:
CPU_FLAG_FPU	A Floating Point Unit (FPU)
CPU_FLAG_MMU	A Memory Management Unit (MMU), and the MMU is enabled (i.e., the CPU is currently in virtual addressing mode)
ARM_CPU_FLAG_CC_INCR_BIT_32	A 32-bit clock cycle counter (CLOCKCYCLES_INCR_BIT is 32)
ARM_CPU_FLAG_IDIV	H/W division: the `UDIV` and `SDIV` instructions are supported
ARM_CPU_FLAG_LPAE	Large Physical Address Extension support is enabled
ARM_CPU_FLAG_NEON	NEON technology, a 128-bit SIMD architecture extension to the ARM Cortex-A series processor
ARM_CPU_FLAG_SMP	Multiple processors
ARM_CPU_FLAG_V7	ARMv7 architecture
ARM_CPU_FLAG_V7_MP	ARMv7 multiprocessor extensions
ARM_CPU_FLAG_V7_MP_ERRATA	Needs SMP TLB workarounds
ARM_CPU_FLAG_VFP_D32	VFP has 32 double registers
ARM_CPU_FLAG_WMMX2	An iWMMX2 coprocessor
ARM_CPU_FLAG_XSCALE_CP0	Xscale CP0 MAC unit
AARCH64_CPU_ACTLR	Auxiliary Control Register
AARCH64_CPU_FLAG_CC_INCR_32	A 32-bit clock cycle counter (CLOCKCYCLES_INCR_BIT is 32)
AARCH64_CPU_FLAG_KRYO_TLB	The system needs to use the workaround for the Qualcomm Technologies Falkor/Kryo erratum 1003 or the Qualcomm Falkor errata 1009 for Kryo. If your target needs to use this workaround, you must manually set this flag using the -F option for startup-*.
AARCH64_CPU_FLAG_LSE	The system supports the Large System Extension; see “LL/SC vs LSE atomic operations,” below
AARCH64_CPU_FLAG_SMP	Multiple processors
AARCH64_CPU_FLAG_SIMD	NEON technology, a 128-bit SIMD architecture extension to the ARM Cortex-A series processor
AARCH64_CPU_FLAG_VHE	ARM v8.1 and more recent. Support virtualization host extensions (VHE).
AARCH64_CPU_PAUTH	CPU supports Pointer Authentication (ARM v8.3 and more recent). This flag is set using the -U option for startup-*. When -U is specified, the kernel checks each CPU to determine if it supports Pointer Authentication and then sets AARCH64_CPU_PAUTH for CPUs that support it.
AARCH64_CPU_SSBS	If this flag is set for CPU 0, the kernel checks each CPU to determine whether it supports FEAT_SSBS (Speculative Store Bypass Safe (SSBS)). To determine whether a CPU supports SSBS, the kernel queries the CPU's ID_AA64PFR1_EL1 feature register (not its `cpuinfo` entry). If the CPU supports SSBS, its PSTATE.SSBS bit is set. A CPU's PSTATE.SSBS bit is not cleared if AARCH64_CPU_SSBS is not set for `cpuinfo` for CPU 0.
X86_64_CPU_AVX	Advanced Vector Extensions
X86_64_CPU_BSWAP	`BSWAP` instruction
X86_64_CPU_CMOV	`CMOVxx` instructions
X86_64_CPU_CPUID	`CPUID` instruction
X86_64_CPU_FXSR	`FXSAVE/FXRSTOR` instructions
X86_64_CPU_INVARIANT_TSC	Invariant (constant) Time Stamp Counter
X86_64_CPU_INVLPG	`INVLPG` instruction
X86_64_CPU_MMX	MMX instructions
X86_64_CPU_MTRR	MTRR (Memory Type Range Register) registers
X86_64_CPU_NX	No-eXecute PTE bit
X86_64_CPU_PAE	Extended addressing
X86_64_CPU_PAT	Page Attribute Tables
X86_64_CPU_PCID	Process-Context Identifiers
X86_64_CPU_PGE	TLB global mappings
X86_64_CPU_PSE	Needs TLB flush when splitting a large page
X86_64_CPU_PTESPLIT_TLBFLUSH	Page size extensions
X86_64_CPU_RDTSC	`RDTSC` instruction
X86_64_CPU_SEP	`SYSENTER` and `SYSEXIT` instructions
X86_64_CPU_SIMD	SIMD instructions
X86_64_CPU_SSE2	Streaming SIMD Extensions 2
X86_64_CPU_XSAVE	`XSAVE` and `XRSTOR` instructions
X86_64_CPU_WP	`WP` bit in the `CR0` register

LL/SC vs LSE atomic operations

The ARMv8-A architecture (see https://developer.arm.com/documentation/ddi0487/latest/) provides two groups of opcodes for atomic operations:

standard load-link/store conditional (LLSC)
ARMv8.1-A Large System Extension (LSE)

On the 64-bit ARM variant of procnto, if all CPUs support LSE atomics, the set of QNX-specific atomic functions default to using LSE, otherwise we revert to LLSC. The following QNX Neutrino functions are affected:

Note that pthread_spin_lock() and pthread_spin_trylock() use these atomic functions; pthread_barrier_wait() and pthread_mutex_destroy() also use them, but to a lesser extent.

If all the CPUs in your system support ARMv8.1-A LSE atomics, you can profile these functions using both LLSC and LSE to determine which version gives better performance. On systems that default to LSE, you can revert to using LLSC by clearing the AARCH64_CPU_FLAG_LSE flag in the system page by either temporarily modifying the startup, or if the startup supports the -F option, clearing the CPU flag by passing -F~0x8000 to startup.

Note that the set of C11-specific atomic functions (such as atomic_fetch_add() in stdatomic.h) use LSE instructions only if you specify -march==armv8-a+lse or -march=armv8.N (where N is 1 or higher) on the compiler command line. The default is to build for the lowest common denominator ARMv8 instruction set, which doesn't include the LSE instructions.