RFR: 8283199: Linux os::cpu_microcode_revision() stalls cold startup [v3]

[David Holmes]

On Mon, 21 Mar 2022 13:24:47 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> src/hotspot/os_cpu/linux_x86/os_linux_x86.cpp line 467:
>> 
>>> 465: 
>>> 466:   // Attempt 1 (faster): Read the microcode version off the sysfs.
>>> 467:   {
>> 
>> Why the new block?
>
> Because I don't want to extend the lifetime of `fp`, `data`, etc.

I really don't see an issue, only fp needs to change

// Attempt 1 (faster): Read the microcode version off the sysfs.
// No block
FILE *fp = os::fopen("/sys/devices/system/cpu/cpu0/microcode/version", "r");
if (fp) {
  char data[128] = {0}; // looking for short line
  if (fgets(data, sizeof(data), fp)) {
    sscanf(data, "%x", &result);
  }
  fclose(fp);
  if (result != 0) {  // moved inside if block
    return result;
  }
}

// Attempt 2 (slower): Read the microcode version off the procfs.
// No block - reuse fp
fp = os::fopen("/proc/cpuinfo", "r");
if (fp) {
  char data[2048] = {0}; // lines should fit in 2K buf
  size_t len = sizeof(data);
  ...
}

That way the diff would have been the addition of a chunk of new code and a couple of modified lines at the start of the existing block.

-------------

PR: https://git.openjdk.java.net/jdk/pull/7825