AVX-512 components use could cause core turbo frequency drop. So it's useful to expose AVX-512 usage elapsed time as a heuristic hint for the user space job scheduler to cluster the AVX-512 using tasks together.
Example: $ cat /proc/pid/status | grep AVX512_elapsed_ms AVX512_elapsed_ms: 1020 The number '1020' denotes 1020 millisecond elapsed since last time context switch the off-CPU task using AVX-512 components, thus the task could cause core frequency drop. Or: $ cat /proc/pid/status | grep AVX512_elapsed_ms AVX512_elapsed_ms: -1 The number '-1' indicates the task didn't use AVX-512 components before thus unlikely has frequency drop issue. User space tools may want to further check by: $ perf stat --pid <pid> -e core_power.lvl2_turbo_license -- sleep 1 Performance counter stats for process id '3558': 3,251,565,961 core_power.lvl2_turbo_license 1.004031387 seconds time elapsed Non-zero counter value confirms that the task causes frequency drop. Signed-off-by: Aubrey Li <aubrey...@linux.intel.com> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Andi Kleen <a...@linux.intel.com> Cc: Tim Chen <tim.c.c...@linux.intel.com> Cc: Dave Hansen <dave.han...@intel.com> Cc: Arjan van de Ven <ar...@linux.intel.com> --- arch/x86/kernel/fpu/xstate.c | 38 ++++++++++++++++++++++++++++++++++++ fs/proc/array.c | 5 +++++ 2 files changed, 43 insertions(+) diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index 87a57b7642d3..c361de2bfb28 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -7,6 +7,7 @@ #include <linux/cpu.h> #include <linux/mman.h> #include <linux/pkeys.h> +#include <linux/seq_file.h> #include <asm/fpu/api.h> #include <asm/fpu/internal.h> @@ -1245,3 +1246,40 @@ int copy_user_to_xstate(struct xregs_state *xsave, const void __user *ubuf) return 0; } + +/* + * Report the amount of time elapsed in millisecond since last AVX512 + * use in the task. + */ +void avx512_state(struct seq_file *m, struct task_struct *task) +{ + unsigned long timestamp = task->thread.fpu.avx512_timestamp; + long delta; + + if (!timestamp) + 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 CPU specific thread state + */ +void arch_task_state(struct seq_file *m, struct task_struct *task) +{ + /* + * Report AVX512 state if the processor and build option supported. + */ + if (cpu_feature_enabled(X86_FEATURE_AVX512F)) + avx512_state(m, task); +} diff --git a/fs/proc/array.c b/fs/proc/array.c index 0ceb3b6b37e7..dd88c2219f08 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -392,6 +392,10 @@ static inline void task_core_dumping(struct seq_file *m, struct mm_struct *mm) seq_putc(m, '\n'); } +void __weak arch_task_state(struct seq_file *m, struct task_struct *task) +{ +} + int proc_pid_status(struct seq_file *m, struct pid_namespace *ns, struct pid *pid, struct task_struct *task) { @@ -414,6 +418,7 @@ int proc_pid_status(struct seq_file *m, struct pid_namespace *ns, task_cpus_allowed(m, task); cpuset_task_status_allowed(m, task); task_context_switch_counts(m, task); + arch_task_state(m, task); return 0; } -- 2.17.1