For HPC workloads its seen that ondemand cpufreq governor introduces
some jitter. It has been reported in several distros (eg Ubuntu,
Redhat).
Jitter is mainly due to kernel worker threads which needs to get
scheduled to perform load calculation and set frequencies.
A fix that could reduce jitter went into ubuntu recently (only for
ppc64) [1], was by setting a ondemand governor's tuning parameter
"sampling_down_factor".
Sampling_down_factor is a multiplying factor for sampling rate (rate at
which cpu load calculation happens) when the CPU is at its highest frequency it
reduces the rate at which load calcuations are done.
By setting sampling_down_factor = 100, If cpu reaches max frequency,
the sampling rate is reduced by 100 times which reduces jitter.
Typically, sampling_rate = 10 ms,
sampling_down_factor=100 ,
resulting sampling rate = 1000ms = 1 sec
The idea is that the effect of jitter is more pronounced when the cpu
load is closer to 100%, as ondemand governor sets to max frequency
only when there is high cpu load. We could reduce the sampling rate,
when it effects the most.
This patch adds a new tuned profile "balanced-hpc" which is
derived out of balanced profile. This profile reduces jitter
that is seen with ondemand governor, by setting sampling_down_factor=100.
It uses the command sampling_down_factor introduced in the
previous patch.
Signed-off-by: Akshay Adiga <akshay.adiga(a)linux.vnet.ibm.com>
---
profiles/balanced-hpc/tuned.conf | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
create mode 100644 profiles/balanced-hpc/tuned.conf
diff --git a/profiles/balanced-hpc/tuned.conf b/profiles/balanced-hpc/tuned.conf
new file mode 100644
index 0000000..f6d4a43
--- /dev/null
+++ b/profiles/balanced-hpc/tuned.conf
@@ -0,0 +1,19 @@
+#
+# tuned configuration
+#
+
+[cpu]
+governor=ondemand
+energy_perf_bias=normal
+sampling_down_factor=100
+
+[audio]
+timeout=10
+
+[video]
+radeon_powersave=auto
+
+[disk]
+# Comma separated list of devices, all devices if commented out.
+# devices=sda
+alpm=medium_power
--
2.5.5