From 6418b8c1fbcfdcda4cad8efacccceb7bcdbb1de9 Mon Sep 17 00:00:00 2001
From: Jim Warner <james.warner@comcast.net>
Date: Wed, 20 Mar 2024 00:00:00 -0500
Subject: [PATCH] library: address remaining cpu distortions, <stat> api

When the potential cpu distortion was addressed in the
commit referenced below, the revision did not quite go
far enough.  This was revealed in the merge plus issue
posts also shown. Thus a need for this final solution.

[ and now that all the stat_jifs fields are verified ]
[ that TICsetH macro need not check for distortions. ]

Reference(s):
https://gitlab.com/procps-ng/procps/-/merge_requests/223
https://gitlab.com/procps-ng/procps/-/issues/321

. Mar, 2017 - cpu distorions relocated/improved
commit 253ac7f709412a8699767bd70faeaf98e19614f0

Discovered-by: Chao Liu SuperSix173 <liuchao173@huawei.com>
Signed-off-by: Jim Warner <james.warner@comcast.net>
---
 library/stat.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/library/stat.c b/library/stat.c
index c37e9b54..b04fe0a5 100644
--- a/library/stat.c
+++ b/library/stat.c
@@ -182,9 +182,10 @@ struct stat_info {
 #define SYS_set(e,t,x) setDECL(e) { \
     (void)T; R->result. t = S->new. x; }
 // delta assignment
+// ( thanks to 'stat_derive_unique', this macro no longer needs to )
+// ( protect against a negative value when a cpu is brought online )
 #define TICsetH(e,t,x) setDECL(e) { \
-    (void)S; R->result. t = ( T->new. x - T->old. x ); \
-    if (R->result. t < 0) R->result. t = 0; }
+    (void)S; R->result. t = ( T->new. x - T->old. x ); }
 #define SYSsetH(e,t,x) setDECL(e) { \
     (void)T; R->result. t = ( S->new. x - S->old. x ); }
 
@@ -555,6 +556,9 @@ wrap_up:
 static inline void stat_derive_unique (
         struct hist_tic *this)
 {
+    unsigned long long *new, *old;
+    int i;
+
     /* note: we calculate these derived values in a manner consistent with
              the calculations for cgroup accounting, as nearly as possible
        ( see linux sources: ./kernel/cgroup/rstat.c, root_cgroup_cputime ) */
@@ -576,13 +580,15 @@ static inline void stat_derive_unique (
     this->new.xbsy
         = this->new.xtot - this->new.xidl;
 
-    // don't distort deltas when cpus are taken offline or brought online
-    if (this->new.xusr < this->old.xusr
-    || (this->new.xsys < this->old.xsys)
-    || (this->new.xidl < this->old.xidl)
-    || (this->new.xbsy < this->old.xbsy)
-    || (this->new.xtot < this->old.xtot))
-        memcpy(&this->old, &this->new, sizeof(struct stat_jifs));
+    // don't distort results when cpus are brought back online
+    new = (unsigned long long *)&this->new;
+    old = (unsigned long long *)&this->old;
+    for (i = 0; i < sizeof(struct stat_jifs) / sizeof(unsigned long long); i++) {
+        if (*(new++) < *(old++)) {
+            memcpy(&this->old, &this->new, sizeof(struct stat_jifs));
+            break;
+        }
+    }
 } // end: stat_derive_unique
 
 
-- 
2.33.0

