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

[Baesken, Matthias]

Hi Thomas, interesting idea . David – would you be fine with  what Thomas proposes ?

Best regards, Matthias


From: Thomas Stüfe <thomas.stuefe at gmail.com>
Sent: Mittwoch, 27. März 2019 10:28
To: Baesken, Matthias <matthias.baesken at sap.com>
Cc: hotspot-dev at openjdk.java.net
Subject: Re: RFR: 8221535: add steal tick related information to hs_error file [linux]

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<mailto: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