x86/process: Add AVX-512 usage elapsed time to /proc/pid/arch_status

AVX-512 components usage can result in turbo frequency drop. So it's useful
to expose AVX-512 usage elapsed time as a heuristic hint for user space job
schedulers to cluster the AVX-512 using tasks together.

Examples:
$ while [ 1 ]; do cat /proc/tid/arch_status | grep AVX512; sleep 1; done
AVX512_elapsed_ms:      4
AVX512_elapsed_ms:      8
AVX512_elapsed_ms:      4

This means that 4 milliseconds have elapsed since the tsks AVX512 usage was
detected when the task was scheduled out.

$ cat /proc/tid/arch_status | grep AVX512
AVX512_elapsed_ms:      -1

'-1' indicates that no AVX512 usage was recorded for this task.

The time exposed is not necessarily accurate when the arch_status file is
read as the AVX512 usage is only evaluated when a task is scheduled
out. Accurate usage information can be obtained with performance counters.

[ tglx: Massaged changelog ]

Signed-off-by: Aubrey Li <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: Andy Lutomirski <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linux API <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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