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SubjectRe: [PATCH 1/1] cpufreq: pcc-cpufreq: Re-introduce deadband effect to reduce number of frequency changes
On Wed, Sep 07, 2016 at 10:32:01AM +0530, Viresh Kumar wrote:
> On 01-09-16, 15:21, Andreas Herrmann wrote:

---8<---

> > I started with the value return as "nominal latency" for PCC. This
> > was 300000 ns on the test system and made things worse. I've tested
> > other values as well unitl I've found a local optimium at 45000ns but
> > performance was lower in comparison to when I've applied my hack.
>
> Can you try to use kernel tracer (ftrace) and see how the frequencies
> are getting changed and at what frequency.

Below is some trace data. I hope it is of some help.

(A) - sampling 10s period when system is idle
(B) - sampling 10s period when system partially loaded (kernel
compilation using 2 jobs)

(1) 4.8-rc5
(2) 4.8-rc5 with my patch (reintro of deadband effect within
pcc-cpufreq)
(3) 4.8-rc5 with reversal of 6393d6a102 (cpufreq: ondemand: Eliminate
the deadband effect)

Let me know whether you are looking for other trace data wrt this
issue.


Thanks,

Andreas

---

(A)-(1)

# Total Lost Samples: 0
# Samples: 41 of event 'power:cpu_frequency'
# Event count (approx.): 41
# Overhead Command Shared Object Symbol
# ........ ............ ................ .............................
39.02% kworker/14:1 [kernel.vmlinux] [k] cpufreq_notify_transition
29.27% kworker/0:0 [kernel.vmlinux] [k] cpufreq_notify_transition
19.51% kworker/10:1 [kernel.vmlinux] [k] cpufreq_notify_transition
7.32% kworker/5:2 [kernel.vmlinux] [k] cpufreq_notify_transition
2.44% kworker/23:2 [kernel.vmlinux] [k] cpufreq_notify_transition
2.44% kworker/40:1 [kernel.vmlinux] [k] cpufreq_notify_transition

(A)-(2)

# Total Lost Samples: 0
# Samples: 6 of event 'power:cpu_frequency'
# Event count (approx.): 6
# Overhead Command Shared Object Symbol
# ........ ............ ................ .............................
33.33% kworker/1:2 [kernel.vmlinux] [k] cpufreq_notify_transition
16.67% kworker/16:1 [kernel.vmlinux] [k] cpufreq_notify_transition
16.67% kworker/22:1 [kernel.vmlinux] [k] cpufreq_notify_transition
16.67% kworker/26:1 [kernel.vmlinux] [k] cpufreq_notify_transition
16.67% kworker/33:1 [kernel.vmlinux] [k] cpufreq_notify_transition

(A)-(3)

# Total Lost Samples: 0
# Samples: 7 of event 'power:cpu_frequency'
# Event count (approx.): 7
# Overhead Command Shared Object Symbol
# ........ ............ ................ .............................
28.57% kworker/58:1 [kernel.vmlinux] [k] cpufreq_notify_transition
14.29% kworker/19:2 [kernel.vmlinux] [k] cpufreq_notify_transition
14.29% kworker/20:2 [kernel.vmlinux] [k] cpufreq_notify_transition
14.29% kworker/22:2 [kernel.vmlinux] [k] cpufreq_notify_transition
14.29% kworker/23:1 [kernel.vmlinux] [k] cpufreq_notify_transition
14.29% kworker/35:1 [kernel.vmlinux] [k] cpufreq_notify_transition

---

(B)-(1)

# Total Lost Samples: 0
# Samples: 2K of event 'power:cpu_frequency'
# Event count (approx.): 2382
# Overhead Command Shared Object Symbol
# ........ ............ ................ .............................
5.75% kworker/0:0 [kernel.vmlinux] [k] cpufreq_notify_transition
4.16% kworker/12:2 [kernel.vmlinux] [k] cpufreq_notify_transition
3.11% kworker/17:1 [kernel.vmlinux] [k] cpufreq_notify_transition
2.94% kworker/2:1 [kernel.vmlinux] [k] cpufreq_notify_transition
2.73% kworker/19:1 [kernel.vmlinux] [k] cpufreq_notify_transition
...

(B)-(2)

# Total Lost Samples: 0
# Samples: 320 of event 'power:cpu_frequency'
# Event count (approx.): 320
# Overhead Command Shared Object Symbol
# ........ ............ ................ .............................
4.69% kworker/56:1 [kernel.vmlinux] [k] cpufreq_notify_transition
4.06% kworker/12:1 [kernel.vmlinux] [k] cpufreq_notify_transition
4.06% kworker/28:1 [kernel.vmlinux] [k] cpufreq_notify_transition
4.06% kworker/6:2 [kernel.vmlinux] [k] cpufreq_notify_transition
3.75% kworker/32:2 [kernel.vmlinux] [k] cpufreq_notify_transition
...

(B)-(3)

# Total Lost Samples: 0
# Samples: 333 of event 'power:cpu_frequency'
# Event count (approx.): 333
# Overhead Command Shared Object Symbol
# ........ ............ ................ .............................
4.80% kworker/51:1 [kernel.vmlinux] [k] cpufreq_notify_transition
4.50% kworker/39:1 [kernel.vmlinux] [k] cpufreq_notify_transition
4.20% kworker/47:1 [kernel.vmlinux] [k] cpufreq_notify_transition
3.90% kworker/59:1 [kernel.vmlinux] [k] cpufreq_notify_transition
3.90% kworker/7:2 [kernel.vmlinux] [k] cpufreq_notify_transition
...

---

With (1) pcc-cpufreq tries to set pretty much every frequency even if
the system is idle, e.g. here is the start of (perf script output)
from (A)-(1):

kworker/5:2 904 [005] 255.778343: power:cpu_frequency: state=1216000 cpu_id=5
kworker/5:2 904 [005] 255.794382: power:cpu_frequency: state=1264000 cpu_id=5
kworker/5:2 904 [005] 256.102400: power:cpu_frequency: state=1200000 cpu_id=5
kworker/10:1 171 [010] 258.010362: power:cpu_frequency: state=2224000 cpu_id=10
kworker/10:1 171 [010] 258.026366: power:cpu_frequency: state=1264000 cpu_id=10
kworker/10:1 171 [010] 258.594514: power:cpu_frequency: state=1200000 cpu_id=10
kworker/10:1 171 [010] 258.618417: power:cpu_frequency: state=1232000 cpu_id=10
kworker/10:1 171 [010] 258.634409: power:cpu_frequency: state=1264000 cpu_id=10
kworker/10:1 171 [010] 258.674467: power:cpu_frequency: state=1200000 cpu_id=10
kworker/10:1 171 [010] 258.730486: power:cpu_frequency: state=1216000 cpu_id=10
kworker/40:1 388 [040] 258.730999: power:cpu_frequency: state=1200000 cpu_id=40
kworker/23:2 775 [023] 258.731504: power:cpu_frequency: state=1200000 cpu_id=23
kworker/14:1 178 [014] 258.732013: power:cpu_frequency: state=1216000 cpu_id=14
kworker/10:1 171 [010] 258.906434: power:cpu_frequency: state=1200000 cpu_id=10
kworker/14:1 178 [014] 258.970500: power:cpu_frequency: state=1200000 cpu_id=14
kworker/14:1 178 [014] 258.998440: power:cpu_frequency: state=1232000 cpu_id=14
kworker/14:1 178 [014] 259.034490: power:cpu_frequency: state=1200000 cpu_id=14
kworker/14:1 178 [014] 259.095089: power:cpu_frequency: state=1216000 cpu_id=14
kworker/14:1 178 [014] 259.270470: power:cpu_frequency: state=1200000 cpu_id=14
...

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