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Subject[PATCH v12 3/3] Documentation/filesystems/proc.txt: add AVX512_elapsed_ms
Date
Added AVX512_elapsed_ms in /proc/<pid>/status. Report it
in Documentation/filesystems/proc.txt

Signed-off-by: Aubrey Li <aubrey.li@linux.intel.com>
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>
---
Documentation/filesystems/proc.txt | 28 +++++++++++++++++++++++++++-
1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 66cad5c86171..425f2f09c9aa 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -45,6 +45,7 @@ Table of Contents
3.9 /proc/<pid>/map_files - Information about memory mapped files
3.10 /proc/<pid>/timerslack_ns - Task timerslack value
3.11 /proc/<pid>/patch_state - Livepatch patch operation state
+ 3.12 /proc/<pid>/AVX512_elapsed_ms - time elapsed since last AVX512 use

4 Configuring procfs
4.1 Mount options
@@ -207,6 +208,7 @@ read the file /proc/PID/status:
Speculation_Store_Bypass: thread vulnerable
voluntary_ctxt_switches: 0
nonvoluntary_ctxt_switches: 1
+ AVX512_elapsed_ms: 8

This shows you nearly the same information you would get if you viewed it with
the ps command. In fact, ps uses the proc file system to obtain its
@@ -224,7 +226,7 @@ asynchronous manner and the value may not be very precise. To see a precise
snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
It's slow but very precise.

-Table 1-2: Contents of the status files (as of 4.19)
+Table 1-2: Contents of the status files (as of 5.1)
..............................................................................
Field Content
Name filename of the executable
@@ -289,6 +291,7 @@ Table 1-2: Contents of the status files (as of 4.19)
Mems_allowed_list Same as previous, but in "list format"
voluntary_ctxt_switches number of voluntary context switches
nonvoluntary_ctxt_switches number of non voluntary context switches
+ AVX512_elapsed_ms time elapsed since last AVX512 use in millisecond
..............................................................................

Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
@@ -1948,6 +1951,29 @@ patched. If the patch is being enabled, then the task has already been
patched. If the patch is being disabled, then the task hasn't been
unpatched yet.

+3.12 /proc/<pid>/AVX512_elapsed_ms - time elapsed since last AVX512 use
+--------------------------------------------------------------------------
+If AVX512 is supported on the machine, this file displays time elapsed since
+last AVX512 usage of the task in millisecond.
+
+The per-task AVX512 usage tracking mechanism is added during context switch.
+When the task is scheduled out, the AVX512 timestamp of the task is tagged
+by jiffies if AVX512 usage is detected.
+
+When this interface is queried, AVX512_elapsed_ms is calculated as follows:
+
+ delta = (long)(jiffies_now - AVX512_timestamp);
+ AVX512_elpased_ms = jiffies_to_msecs(delta);
+
+Because this tracking mechanism depends on context switch, the number of
+AVX512_elapsed_ms could be inaccurate if the AVX512 using task runs alone on
+a CPU and not scheduled out for a long time. An extreme experiment shows a
+task is spinning on the AVX512 ops on an isolated CPU, but the longest elapsed
+time is close to 4 seconds(HZ = 250).
+
+So 5s or even longer is an appropriate threshold for the job scheduler to poll
+and decide if the task should be classifed as an AVX512 task and migrated
+away from the core on which a Non-AVX512 task is running.

------------------------------------------------------------------------------
Configuring procfs
--
2.17.1
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