I3status-rust: load block fails to get cpu count

[Thra11]

        let f = File::open("/proc/cpuinfo")
            .block_error("load", "Your system doesn't support /proc/cpuinfo")?;
        let f = BufReader::new(f);

        let mut logical_cores = 0;

        for line in f.lines().scan((), |_, x| x.ok()) {
            // TODO: Does this value always represent the correct number of logical cores?
            if line.starts_with("siblings") {
                let split: Vec<&str> = (&line).split(' ').collect();
                logical_cores = split[1]
                    .parse::<u32>()                                                                                                                           
                    .block_error("load", "Invalid Cpu info format!")?;                                                                                        
                break;                                                                                                                                        
            }                                                                                                                                                 
        }

My system supports /proc/cpuinfo, but it doesn't have any lines starting with siblings. The format may have changed (I'm now on linux kernel 5.7.0).

Reading /sys/devices/system/cpu/present might be a better alternative. On my system, its value is 0-5, I believe representing the fact that the six CPUs numbered 0 to 5 are all present. The fact it doesn't just say 6 might make it a little more complicated to parse.

Other options include calling lscpu (although that requires that util-linux is installed), or delegating the task to another crate, such as cpuinfo (I have created PR #748 which would fix this issue by using the cpuinfo crate).

Also, if we still can't find the number of CPUs, 1 might be a more sensible value than 0.

[atheriel]

A robust solution would be to find out how lscpu actually works and treat that as gospel. The source is here: https://git.kernel.org/pub/scm/utils/util-linux/util-linux.git/tree/ but I haven't been able to find it with a quick look around.

[Thra11]

I believe the journey starts here, with relevant bits here and here and here.

Haven't read through all of it yet, but I get the impression it's basically reading /sys/devices/system/cpu/present and doing stuff with the "cpu set" that it represents.

[ammgws]

@Thra11 If #859 didn't fix this for you then please re-open

[Thra11]

Having updated to HEAD, currently "idling" at 18.31 load, so something's not quite right.

[Thra11]

Will try to debug it. Btw, I don't appear to have the option to reopen this.

[Thra11]

Hmmm. Looks like it's probably correct actually, my system's just too busy to get anywhere near the default thresholds at the moment. It is correctly dividing 18.31 by 6 logical cores to get a used_perc of 3.05, which is way over the default critical value of 0.9, but appears to be correct.