linux-kernel - [PATCH v17 3/3] Documentation/filesystems/proc.txt: add arch

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Message-Id: <20190421183529.9141-3-aubrey.li@linux.intel.com>
Date:   Mon, 22 Apr 2019 02:35:29 +0800
From:   Aubrey Li <aubrey.li@...ux.intel.com>
To:     tglx@...utronix.de, mingo@...hat.com, peterz@...radead.org,
        hpa@...or.com
Cc:     ak@...ux.intel.com, tim.c.chen@...ux.intel.com,
        dave.hansen@...el.com, arjan@...ux.intel.com, adobriyan@...il.com,
        akpm@...ux-foundation.org, aubrey.li@...el.com,
        linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v17 3/3] Documentation/filesystems/proc.txt: add arch_status file

Added /proc/<pid>/arch_status file, and added AVX512_elapsed_ms in
/proc/<pid>/arch_status. Report it in Documentation/filesystems/proc.txt

Signed-off-by: Aubrey Li <aubrey.li@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Alexey Dobriyan <adobriyan@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Linux API <linux-api@...r.kernel.org>
---
 Documentation/filesystems/proc.txt | 37 ++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 66cad5c86171..cf5114a8fb13 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>/arch_status - Task architecture specific information
 
   4	Configuring procfs
   4.1	Mount options
@@ -1948,6 +1949,42 @@ 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>/arch_status - task architecture specific status
+-------------------------------------------------------------------
+When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the
+architecture specific status of the task.
+
+Example
+-------
+ $ cat /proc/6753/arch_status
+ AVX512_elapsed_ms:      8
+
+Description
+-----------
+
+ AVX512_elapsed_ms:
+ ------------------
+  If AVX512 is supported on the machine, this entry shows the milliseconds
+  elapsed since the last time AVX512 usage was recorded. The recording
+  happens on a best effort basis when a task is scheduled out. This means
+  that the value depends on two factors:
+
+    1) The time which the task spent on the CPU without being scheduled
+       out. With CPU isolation and a single runnable task this can take
+       several seconds.
+
+    2) The time since the task was scheduled out last. Depending on the
+       reason for being scheduled out (time slice exhausted, syscall ...)
+       this can be arbitrary long time.
+
+  As a consequence the value cannot be considered precise and authoritative
+  information. The application which uses this information has to be aware
+  of the overall scenario on the system in order to determine whether a
+  task is a real AVX512 user or not.
+
+  A special value of '-1' indicates that no AVX512 usage was recorded, thus
+  the task is unlikely an AVX512 user, but depends on the workload and the
+  scheduling scenario, it also could be a false negative mentioned above.
 
 ------------------------------------------------------------------------------
 Configuring procfs
-- 
2.17.1