Commit 0c608dad authored Jun 06, 2019 by Aubrey Li Committed by Thomas Gleixner Jun 12, 2019

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 <aubrey.li@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: akpm@linux-foundation.org
Cc: peterz@infradead.org
Cc: hpa@zytor.com
Cc: ak@linux.intel.com
Cc: tim.c.chen@linux.intel.com
Cc: dave.hansen@intel.com
Cc: arjan@linux.intel.com
Cc: adobriyan@gmail.com
Cc: aubrey.li@intel.com
Cc: linux-api@vger.kernel.org
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linux API <linux-api@vger.kernel.org>
Link: https://lkml.kernel.org/r/20190606012236.9391-2-aubrey.li@linux.intel.com

parent 68bc30bb

arch/x86/Kconfig

+1 −0

Original line number	Diff line number	Diff line
		@@ -217,6 +217,7 @@ config X86
		select USER_STACKTRACE_SUPPORT
		select VIRT_TO_BUS
		select X86_FEATURE_NAMES if PROC_FS
		select PROC_PID_ARCH_STATUS if PROC_FS

		config INSTRUCTION_DECODER
		def_bool y

arch/x86/kernel/fpu/xstate.c

+47 −0

Original line number	Diff line number	Diff line
		@@ -8,6 +8,8 @@
		#include <linux/cpu.h>
		#include <linux/mman.h>
		#include <linux/pkeys.h>
		#include <linux/seq_file.h>
		#include <linux/proc_fs.h>

		#include <asm/fpu/api.h>
		#include <asm/fpu/internal.h>
		@@ -1240,3 +1242,48 @@ int copy_user_to_xstate(struct xregs_state xsave, const void __user ubuf)

		return 0;
		}

		#ifdef CONFIG_PROC_PID_ARCH_STATUS
		/*
		* Report the amount of time elapsed in millisecond since last AVX512
		* use in the task.
		*/
		static void avx512_status(struct seq_file m, struct task_struct task)
		{
		unsigned long timestamp = READ_ONCE(task->thread.fpu.avx512_timestamp);
		long delta;

		if (!timestamp) {
		/*
		* Report -1 if no AVX512 usage
		*/
		delta = -1;
		} else {
		delta = (long)(jiffies - timestamp);
		/*
		* Cap to LONG_MAX if time difference > LONG_MAX
		*/
		if (delta < 0)
		delta = LONG_MAX;
		delta = jiffies_to_msecs(delta);
		}

		seq_put_decimal_ll(m, "AVX512_elapsed_ms:\t", delta);
		seq_putc(m, '\n');
		}

		/*
		* Report architecture specific information
		*/
		int proc_pid_arch_status(struct seq_file m, struct pid_namespace ns,
		struct pid pid, struct task_struct task)
		{
		/*
		* Report AVX512 state if the processor and build option supported.
		*/
		if (cpu_feature_enabled(X86_FEATURE_AVX512F))
		avx512_status(m, task);

		return 0;
		}
		#endif /* CONFIG_PROC_PID_ARCH_STATUS */

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