RFR: 8264412: AArch64: CPU description should refer DMI [v2]

[Gerard Ziemski]

On Wed, 31 Mar 2021 13:23:44 GMT, Yasumasa Suenaga <ysuenaga at openjdk.org> wrote:

>> `jdk.CPUInformation` event on AArch64 has valid CPU description in [JDK-8262491](https://bugs.openjdk.java.net/browse/JDK-8262491), however it does not work on UEFI booted machine.
>> 
>> [JDK-8262491](https://bugs.openjdk.java.net/browse/JDK-8262491) refers device tree to get board name, however it does not exist on UEFI. We need to refer DMI.
>> However we need to have root privilege, so we refer /sys/devices/virtual/dmi/id to avoid it.
>> 
>> We can get board name from /sys/devices/virtual/dmi/id/board_name, but some machine set empty string to it. So we will refer /sys/devices/virtual/dmi/id/product_name as a fallback.
>> 
>> For example, we can get following CPU description on AWS A1 instance after this change:
>> 
>> jdk.CPUInformation {
>>   startTime = 05:28:24.506
>>   cpu = "AArch64"
>>   description = "AArch64 a1.2xlarge  0x41:0x0:0xd08:3, simd, crc, aes, sha1, sha256"
>>   sockets = 8
>>   cores = 8
>>   hwThreads = 8
>> }
>
> Yasumasa Suenaga has updated the pull request incrementally with one additional commit since the last revision:
> 
>   refactoring

2 small nitpicks, but otherwise the functionality of the code looks good to me, though I will have to trust you on using the files to get the CPU description, since I'm no Linux expert:

     "/proc/device-tree/compatible",
     "/sys/devices/virtual/dmi/id/board_name",
     "/sys/devices/virtual/dmi/id/product_name"

src/hotspot/os_cpu/linux_aarch64/vm_version_linux_aarch64.cpp line 174:

> 172:   assert(buf != NULL, "invalid argument");
> 173:   assert(buflen >= 1, "invalid argument");
> 174:   int fd = open(fname, O_RDONLY);

Should be:

` int fd = os::open(fname, O_RDONLY);`

src/hotspot/os_cpu/linux_aarch64/vm_version_linux_aarch64.cpp line 176:

> 174:   int fd = open(fname, O_RDONLY);
> 175:   if (fd != -1) {
> 176:     ssize_t read_sz = read(fd, buf, buflen);

Should be:

`ssize_t read_sz = os::read(fd, buf, buflen);`

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

Changes requested by gziemski (Committer).

PR: https://git.openjdk.java.net/jdk/pull/3259