File lparstat-Fix-negative-values-for-idle-PURR.patch of Package powerpc-utils.37742
From 18a6dbca81b443d3cb7037d8bd39da014b4055ee Mon Sep 17 00:00:00 2001
From: Saket Kumar Bhaskar <skb99@linux.ibm.com>
Date: Mon, 13 Jan 2025 13:43:39 +0530
Subject: [PATCH] lparstat: Fix negative values for %idle PURR
Patch-mainline: expected 1.3.14
Git-commit: 18a6dbca81b443d3cb7037d8bd39da014b4055ee
In certain scenarios, the %idle PURR metric displays negative values [1],
while %busy PURR exceeds 100% giving users false impression of resource
utilisation. This occurs when delta_purr becomes greater than delta_tb,
causing the following expression to yield a negative value, particularly
during 100% system utilization for %idle PURR:
%idle = (delta_tb - delta_purr + delta_idle_purr) / delta_tb * 100;
Without change:
./lparstat -E 1 30
System Configuration
type=Shared mode=Uncapped smt=8 lcpu=20 mem=208057792 kB cpus=42 ent=2.00
---Actual--- -Normalized-
%busy %idle Frequency %busy %idle
------ ------ ------------- ------ ------
103.88 -3.88 2.75GHz[ 98%] 101.80 0.00
103.46 -3.46 2.67GHz[ 95%] 98.28 1.49
101.53 -1.53 2.74GHz[ 98%] 99.50 0.51
103.41 -3.41 2.70GHz[ 96%] 99.27 0.37
The delta_tb is computed using get_scaled_tb, which calculates the
timebase for a given time difference. Previously, nanoseconds were
ignored in the calculation of time difference, which led to delta_tb
being underestimated.
This patch addresses the issue by incorporating nanoseconds into the
time difference, ensuring precise calculations.
Also, rename get_time() to get_time_ns() to denote it returns time in
nanoseconds. get_delta_time() is introduced as a wrapper to get delta
time in seconds.
With change:
./lparstat -E 1 30
System Configuration
type=Shared mode=Uncapped smt=8 lcpu=20 mem=208057792 kB cpus=42 ent=2.00
---Actual--- -Normalized-
%busy %idle Frequency %busy %idle
------ ------ ------------- ------ ------
99.52 0.48 2.74GHz[ 98%] 97.53 2.66
99.53 0.47 2.71GHz[ 97%] 96.54 3.67
99.49 0.51 2.71GHz[ 97%] 96.51 3.87
99.51 0.49 2.70GHz[ 97%] 96.53 3.90
99.48 0.52 2.69GHz[ 96%] 95.50 4.38
[1] https://github.com/ibm-power-utilities/powerpc-utils/issues/103
Signed-off-by: Saket Kumar Bhaskar <skb99@linux.ibm.com>
Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>
---
src/lparstat.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)
diff --git a/src/lparstat.c b/src/lparstat.c
index fe8b0fc..db22316 100644
--- a/src/lparstat.c
+++ b/src/lparstat.c
@@ -254,7 +254,7 @@ long long get_delta_value(char *se_name)
return (value - old_value);
}
-void get_time()
+void get_time_ns(void)
{
struct sysentry *se;
struct timespec ts;
@@ -266,7 +266,12 @@ void get_time()
se = get_sysentry("time");
sprintf(se->value, "%lld",
- (long long)ts.tv_sec);
+ (long long)ts.tv_sec * 1000000000LL + (long long)ts.tv_nsec);
+}
+
+double get_delta_time(void)
+{
+ return (get_delta_value("time") / 1000000000.0);
}
int get_time_base()
@@ -307,7 +312,7 @@ double get_scaled_tb(void)
se = get_sysentry("online_cores");
online_cores = atoi(se->value);
- elapsed = get_delta_value("time");
+ elapsed = get_delta_time();
se = get_sysentry("timebase");
timebase = atoi(se->value);
@@ -386,7 +391,7 @@ void get_cpu_physc(struct sysentry *unused_se, char *buf)
physc = delta_purr / delta_tb;
} else {
- elapsed = get_delta_value("time");
+ elapsed = get_delta_time();
se = get_sysentry("timebase");
timebase = atoi(se->value);
@@ -415,7 +420,7 @@ void get_cpu_app(struct sysentry *unused_se, char *buf)
float timebase, app, elapsed_time;
long long new_app, old_app;
- elapsed_time = get_delta_value("time");
+ elapsed_time = get_delta_time();
se = get_sysentry("timebase");
timebase = atof(se->value);
@@ -1018,7 +1023,7 @@ void init_sysdata(void)
{
int rc = 0;
- get_time();
+ get_time_ns();
parse_lparcfg();
parse_proc_stat();
parse_proc_ints();
--
2.47.1
