RFR: JDK-8301661: Enhance os::pd_print_cpu_info on macOS and Windows [v5]

[David Holmes]

On Thu, 16 Feb 2023 09:18:58 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

>> Enhance os::pd_print_cpu_info on macOS and Windows by information about CPU frequency and caches.
>> On Windows , this info can be obtained by the Processor Power Information API or "powerbase" (CallNtPowerInformation , see https://learn.microsoft.com/en-us/windows/win32/api/powerbase/nf-powerbase-callntpowerinformation ); this is available since Windows Server 2003/XP.
>> On macOS, sysctlbyname can be used.
>
> Matthias Baesken has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Do not print idle state infos on Windows, print same MHz values for all proces only once

General approach seems okay. A couple of queries and nits.

Thanks.

src/hotspot/os/windows/os_windows.cpp line 1900:

> 1898: 
> 1899:   size_t sz_check = sizeof(PROCESSOR_POWER_INFORMATION) * (size_t)proc_count;
> 1900:   NTSTATUS status = ::CallNtPowerInformation(ProcessorInformation, NULL, 0, buf, (ULONG) buflen);

How is the caller supposed to know what size buffer to pass? Are they just supposed to guess and hope it is big enough??

src/hotspot/os/windows/os_windows.cpp line 1901:

> 1899:   size_t sz_check = sizeof(PROCESSOR_POWER_INFORMATION) * (size_t)proc_count;
> 1900:   NTSTATUS status = ::CallNtPowerInformation(ProcessorInformation, NULL, 0, buf, (ULONG) buflen);
> 1901:   int MaxMhz = -1, CurrentMhz = -1, MhzLimit = -1;

Nit: variable names should not start with Capital letters

src/hotspot/os/windows/os_windows.cpp line 1915:

> 1913:             CurrentMhz != (int) pppi->CurrentMhz ||
> 1914:             MhzLimit != (int) pppi->MhzLimit) {
> 1915:           same_vals_for_all_cpus = false;

You could break once this is false.

src/hotspot/os/windows/os_windows.cpp line 1919:

> 1917:       }
> 1918:       // avoid iteration in case buf is too small to hold all proc infos
> 1919:       if (sz_check > buflen) break;

In this case shouldn't the function have returned `STATUS_BUFFER_TOO_SMALL`?

src/hotspot/os/windows/os_windows.cpp line 1924:

> 1922: 
> 1923:     if (same_vals_for_all_cpus && MaxMhz != -1) {
> 1924:       st->print_cr("ProcessorInformation for all %d processors :", proc_count);

Nit: Processor Information

src/hotspot/os/windows/os_windows.cpp line 1931:

> 1929:     pppi = (PROCESSOR_POWER_INFORMATION*) buf;
> 1930:     for (int i = 0; i < proc_count; i++) {
> 1931:       st->print_cr("ProcessorInformation for processor %d", (int) pppi->Number);

Nit: Processor Information

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PR: https://git.openjdk.org/jdk/pull/12403