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
