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library: allow negative system DELTA stats, <STAT> api

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All TIC delta fields are checked for possible negative
results and set to zero when found. This is done so as
to protect against potential anomalies which depend on
kernel version and/or toggling cpus offline or online.

[ it's probably unnecessary with the latest kernels, ]
[ except for iowait. documentation suggests it might ]
[ decrease which would then create a negative delta. ]

The same approach is employed for most of the 'system'
deltas (ctxt, intr & procs_created). However, with two
of the fields (procs_blocked & procs_running) negative
results were allowed. But it now seems such a division
is unwise so this patch will allow all to go negative.

[ rather than force any 'system' delta value to show ]
[ what's logical, we'll now let all reflect reality. ]

Signed-off-by: Jim Warner <james.warner@comcast.net>
This commit is contained in:
Jim Warner 2019-12-13 00:00:00 -05:00 committed by Craig Small
parent 5c37e2d42d
commit 12b6452135
1 changed files with 3 additions and 4 deletions
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7
proc/stat.c
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@ -154,8 +154,7 @@ struct stat_info {
(void)S; R->result. t = ( T->new. x - T->old. x ); \
if (R->result. t < 0) R->result. t = 0; }
#define SYSsetH(e,t,x) setDECL(e) { \
(void)T; R->result. t = ( S->new. x - S->old. x ); \
if (R->result. t < 0) R->result. t = 0; }
(void)T; R->result. t = ( S->new. x - S->old. x ); }
setDECL(noop) { (void)R; (void)S; (void)T; }
setDECL(extra) { (void)S; (void)T; R->result.ull_int = 0; }
@ -207,9 +206,9 @@ SYS_set(SYS_TIME_OF_BOOT, ul_int, btime)
SYSsetH(SYS_DELTA_CTX_SWITCHES, s_int, ctxt)
SYSsetH(SYS_DELTA_INTERRUPTS, s_int, intr)
setDECL(SYS_DELTA_PROC_BLOCKED) { (void)T; R->result.s_int = S->new.procs_blocked - S->old.procs_blocked; }
SYSsetH(SYS_DELTA_PROC_BLOCKED, s_int, procs_blocked)
SYSsetH(SYS_DELTA_PROC_CREATED, s_int, procs_created)
setDECL(SYS_DELTA_PROC_RUNNING) { (void)T; R->result.s_int = S->new.procs_running - S->old.procs_running; }
SYSsetH(SYS_DELTA_PROC_RUNNING, s_int, procs_running)
#undef setDECL
#undef TIC_set