RFR: 8221535: add steal tick related information to hs_error file [linux]

[Thomas Stüfe]

Hi Matthias,

this is a lot of coding for just one counter...

Also os_perf_linux.cpp does something very similar. However, that code does
not get the steal ticks you want, does not seem to care about kernel
differences and could also be improved.

Proposal: Why do you not tweak your new API to be a general purpose API to
read all ticks from /proc/stat. That would be way more useful. Later, if we
feel like it, could change os_perf_linux.cpp to use your function.

We did something similar for the statistical history in the SapMachine, see

https://github.com/SAP/SapMachine/blob/sapmachine/src/hotspot/os/linux/stathist_linux.cpp

. So I would suggest to have a function reading proc stat and returning all
values in a struct. That struct should have provisions for "value not
found" since which values you get depends in kernel version.

--------

Example:

struct value_t { bool valid; uint64_t v; }

struct cpu_values_t {
 value_t user;
 value_t nice;
 value_t system;
 value_t idle;
 value_t iowait;
 value_t steal;
 value_t guest;
 value_t guest_nice;
};

void parse_proc_stat_cpu_line(const char* line, cpu_values_t* out) {
  // Note: existence of some of these values depends on kernel version
  out->user.valid = out->nice.valid = out->system.valid = out->idle.valid =
out->iowait.valid = out->steal.valid = out->guest.valid =
out->guest_nice.valid = false;
  int user, nice, system, idle, iowait, irq, softirq, steal, guest,
guest_nice;
  int num = ::sscanf(line, "cpu %d %d %d %d %d %d %d %d %d %d",
                              &user, &nice, &system, &idle, &iowait, &irq,
&softirq, &steal, &guest, &guest_nice);
  if (num >= 4) {
    out->user.v = user; out->user.valid = true;
    out->nice.v = nice; out->nice.valid = true;
    out->system.v = system; out->system.valid = true;
    out->idle.v = idle; out->idle.valid = true;
    if (num >= 5) { // iowait (5) (since Linux 2.5.41)
      out->iowait = iowait; out->iowait.valid = true;
      if (num >= 8) { // steal (8) (since Linux 2.6.11)
        out->steal = steal; out->steal.valid = true;
        if (num >= 9) { // guest (9) (since Linux 2.6.24)
          out->guest = guest; out->guest.valid = true;
          if (num >= 10) { // guest (9) (since Linux 2.6.33)
            out->guest_nice = guest_nice; out->guest_nice.valid = true;
          }
      }
   }
}


Cheers Thomas


On Wed, Mar 27, 2019 at 9:42 AM Baesken, Matthias <matthias.baesken at sap.com>
wrote:

> Hello, please review  the  following change .
>
> Recent Linux kernels provide in the /proc filesystem   so called "steal"
> information, see the the proc man page :
>
>   ..
> "there is an eighth column, steal - stolen time, which is the time spent
> in other operating systems when running in a virtualized environment"
>
> The info was useful  in our  internal VM,  when looking into performance
> issues  (especially in virtualized environments), so it should be added to
> the hs_err file .
>
> Bug/webrev :
>
> https://bugs.openjdk.java.net/browse/JDK-8221535
>
> http://cr.openjdk.java.net/~mbaesken/webrevs/8221535.0/
>
>
> Best Regards, Matthias
>
>