std::thread::available_parallelism() return 0

[vnt-dev]

available_parallelism() return 0

I tried this code:

fn main() {
    let num = dbg!(std::thread::available_parallelism());
    println!("available_parallelism={:?}",num);
   println!("core num = {:?}",std::thread::available_parallelism());
}

rustc --version --verbose:

rustc 1.73.0-nightly (d8899c577 2023-07-11)
binary: rustc
commit-hash: d8899c577bc11308a0db96e8378373be93330a8f
commit-date: 2023-07-11
host: x86_64-unknown-linux-gnu
release: 1.73.0-nightly
LLVM version: 16.0.5

cat /proc/cpuinfo

cat /proc/cpuinfo
system type		: MT7621
machine			: TGNET_RN1150W
processor		: 0
cpu model		: MIPS 1004Kc V2.15
BogoMIPS		: 583.68
wait instruction	: yes
microsecond timers	: yes
tlb_entries		: 32
extra interrupt vector	: yes
hardware watchpoint	: yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa			: mips1 mips2 mips32r1 mips32r2
ASEs implemented	: mips16 dsp mt
shadow register sets	: 1
kscratch registers	: 0
core			: 0
VPE			: 0
VCED exceptions		: not available
VCEI exceptions		: not available

processor		: 1
cpu model		: MIPS 1004Kc V2.15
BogoMIPS		: 583.68
wait instruction	: yes
microsecond timers	: yes
tlb_entries		: 32
extra interrupt vector	: yes
hardware watchpoint	: yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa			: mips1 mips2 mips32r1 mips32r2
ASEs implemented	: mips16 dsp mt
shadow register sets	: 1
kscratch registers	: 0
core			: 0
VPE			: 1
VCED exceptions		: not available
VCEI exceptions		: not available

processor		: 2
cpu model		: MIPS 1004Kc V2.15
BogoMIPS		: 583.68
wait instruction	: yes
microsecond timers	: yes
tlb_entries		: 32
extra interrupt vector	: yes
hardware watchpoint	: yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa			: mips1 mips2 mips32r1 mips32r2
ASEs implemented	: mips16 dsp mt
shadow register sets	: 1
kscratch registers	: 0
core			: 1
VPE			: 0
VCED exceptions		: not available
VCEI exceptions		: not available

processor		: 3
cpu model		: MIPS 1004Kc V2.15
BogoMIPS		: 583.68
wait instruction	: yes
microsecond timers	: yes
tlb_entries		: 32
extra interrupt vector	: yes
hardware watchpoint	: yes, count: 4, address/irw mask: [0x0ffc, 0x0ffc, 0x0ffb, 0x0ffb]
isa			: mips1 mips2 mips32r1 mips32r2
ASEs implemented	: mips16 dsp mt
shadow register sets	: 1
kscratch registers	: 0
core			: 1
VPE			: 1
VCED exceptions		: not available
VCEI exceptions		: not available

uname -a
Linux Router 3.10.14 #2 SMP Fri Oct 19 18:02:45 CST 2018 mips GNU/Linux

[Urgau]

Looking at the relevant code, it appears that if lib::CPU_COUNT returned 0 it would indeed be a problem, but why would that be?

rust/library/std/src/sys/unix/thread.rs

Line 325 in 56e1aaa

let count = libc::CPU_COUNT(&set) as usize;

Could you try to run this small program, and return us the output of it?

fn main() {
    let mut set: libc::cpu_set_t = unsafe { std::mem::zeroed() };
    unsafe {
        if dbg!(libc::sched_getaffinity(0, std::mem::size_of::<libc::cpu_set_t>(), &mut set)) == 0 {
            dbg!(libc::CPU_COUNT(&set));
        }
    }
}

If it prints out 0 for the CPU_COUNT could you also attach dbg!(&set).

@rustbot label +T-libs +I-prioritize +O-linux -needs-triage

[vnt-dev]

[saethlin]

Can you post the output of running your test program with strace -f ./core_test? I'm just hoping you have some way to get strace onto this router 🙏

[Urgau]

Right, that's what I thought. Let's try to pin point where the bug is by trying the same thing in C.

Could you try to run this small program, and return us the output of it?

#define _GNU_SOURCE
#include <sched.h>
#include <stdio.h>

int main() {
    cpu_set_t set;

    printf("sizeof(set) = %d\n", sizeof(set));

    int ret = sched_getaffinity(0, sizeof(set), &set);
    printf("sched_getaffinity = %d\n", ret);

    int count = CPU_COUNT(&set);
    printf("CPU_COUNT(&set) = %d\n", count);

    return 0;
}

[vnt-dev]

I think for any reason, when the value of 'CPU_COUNT' is 0, 'available_parallelism' should return Err

[vnt-dev]

Sorry, I don't know how to compile C program onto the router

[Urgau]

I think for any reason, when the value of 'CPU_COUNT' is 0, 'available_parallelism' should return Err

Well yes, but we shouldn't get 0 for starter.

Sorry, I don't know how to compile C program onto the router

Hum, that's a bummer. Then I don't know how to debug this further.

[vnt-dev]

Can you provide the compiled binary for me to run? The system environment has been given