[RFC PATCH] tools/power turbostat: Do not print negative LPI residency

[Chen Yu]

turbostat prints the abnormal SYS%LPI across suspend-to-idle:
SYS%LPI = 114479815993277.50

This is reproduced by:
Run a freeze cycle, e.g. "sleepgraph -m freeze -rtcwake 15".
Then do a reboot. After boot up, launch the suspend-idle-idle
and check the SYS%LPI field.

The slp_so residence counter is in LPIT table, and BIOS does not
clears this register across reset. The PMC expects the OS to calculate
the LPI residency based on the delta. However, there is an firmware
issue that the LPIT gets cleared to 0 during the second suspend
to idle after the reboot, which brings negative delta value.

Prints a simple 0 to indicate this error to not confuse the user.

Reported-by: Todd Brandt <todd.e.brandt@xxxxxxxxx>
Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
---
 tools/power/x86/turbostat/turbostat.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/tools/power/x86/turbostat/turbostat.c b/tools/power/x86/turbostat/turbostat.c
index 9a10512e3407..3fa5f9a0218a 100644
--- a/tools/power/x86/turbostat/turbostat.c
+++ b/tools/power/x86/turbostat/turbostat.c
@@ -1472,8 +1472,16 @@ int delta_package(struct pkg_data *new, struct pkg_data *old)
 	old->pc8 = new->pc8 - old->pc8;
 	old->pc9 = new->pc9 - old->pc9;
 	old->pc10 = new->pc10 - old->pc10;
-	old->cpu_lpi = new->cpu_lpi - old->cpu_lpi;
-	old->sys_lpi = new->sys_lpi - old->sys_lpi;
+	if (new->cpu_lpi > old->cpu_lpi) {
+		old->cpu_lpi = new->cpu_lpi - old->cpu_lpi;
+	} else {
+		old->cpu_lpi = 0;
+	}
+	if (new->sys_lpi > old->sys_lpi) {
+		old->sys_lpi = new->sys_lpi - old->sys_lpi;
+	} else {
+		old->sys_lpi = 0;
+	}
 	old->pkg_temp_c = new->pkg_temp_c;
 
 	/* flag an error when rc6 counter resets/wraps */
-- 
2.25.1