Power Management Device Latencies Measurement

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==Kernel patches & build==
==Kernel patches & build==
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Some kernel changes are required for the kernel instrumentation. The patches and config are attached to this page
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Some kernel changes are required for the kernel instrumentation. The patches and config are attached to this page.
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* Starting point: linux-omap master branch at commit [http://git.kernel.org/?p=linux/kernel/git/tmlind/linux-omap-2.6.git;a=commit;h=a83d12a47c9a8c78a184910150797045d69a1570 a83d12a47c9a8c78a184910150797045d69a1570]: ''Linux-omap rebuilt: Updated to v2.6.36, add 24xx uart fix''
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* Starting point: linux-omap master branch as of Sep 2 2011.
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* khilman's patch to fix the low power mode: [http://git.kernel.org/?p=linux/kernel/git/khilman/linux-omap-pm.git;a=commitdiff;h=20b9e9aa97cf811e799420b9096235eb67ef6191 1e91c5f70da4d7d108cbcf026164d001e0e688b3]: ''OMAP: bus-level PM: enable use of runtime PM API for suspend/resume''
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* Experimental workaround to allow the system idle
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''a5a24bc82d3f98758f8fdd0cb0af71012b735477 OMAP-cpuidle-workaround''
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* Tracing instrumentation patches
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** ''12b76fd7076ecd34ff06158e2c3665b300711b3c tracing, perf: add more power related events''
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** ''70ead0e9b0564b4be57acf3c3e063b7b620a2a5b perf: add suspend tracepoint calls''
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** ''d9772cd41e16fec5ff60e89e8100baa027835d7b OMAP3: clean up ASM idle code''
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** ''d26180bc52b62daa25b94ae6cd93cd521e1ba17b OMAP3: add low power entry/exit latency trace points''
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* GPIO instrumentation
* GPIO instrumentation
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The following tables gives the results for the sleep and wake-up latencies for the C-states:
The following tables gives the results for the sleep and wake-up latencies for the C-states:
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image sleep
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[[File:C_states_sleep_latency.png|center|thumb|840px]]
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image wake-up
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[[File:C_states_wake_up_latency.png|center|thumb|840px]]
Note: in the linux code there is no C7/C8/C9 as in the table. C7 is MPU OFF + CORE OFF, which is identical to C9 in the table.
Note: in the linux code there is no C7/C8/C9 as in the table. C7 is MPU OFF + CORE OFF, which is identical to C9 in the table.
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A model with the energy spent in the C-states has been built from the measured numbers. Here is the graph of the energy vs time:
A model with the energy spent in the C-states has been built from the measured numbers. Here is the graph of the energy vs time:
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image graph
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[[File:C_states_os_idle_energy.png|center|thumb|840px]]
Taking the minimum energy from the graph allows to identify the 4 energy-wise interesting C-states: C1, C3, C5, C9 and the threshold time for those C-states to be efficient:
Taking the minimum energy from the graph allows to identify the 4 energy-wise interesting C-states: C1, C3, C5, C9 and the threshold time for those C-states to be efficient:
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image table 4 C-states
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[[File:C_states_data.png|center|thumb|840px]]
Notes:
Notes:
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From the various sources of data the following figures are used:
From the various sources of data the following figures are used:
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==Links==
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===Device latency patches===
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[http://marc.info/?l=linux-omap&m=131350222432043&w=2 PM QoS device constraint code patches]
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==Device latency patches==
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[http://omappedia.org/wiki/TWL4030_power_scripts T2 scripts information page]
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Device constraint code patches, derived from the timings results and measurements with various low power modes combinations.
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==Attachments==
==Attachments==

Revision as of 09:25, 2 September 2011

Contents

PM Devices constraintes measurements

Introduction

To correctly implement the device latency constraint support it is needed to get accurate measurements of the system low power modes overhead:

This wiki page details the measurements setup and the results. The latency data is to be fed into the constraints latency patches.

Kernel patches & build

Some kernel changes are required for the kernel instrumentation. The patches and config are attached to this page.

Changes: enable IDLE, DSS for Beagle, Initramfs Busybox root FS

HW traces details

The trace points are connected on Beagleboard rev B7.

!Warning! The HW power supplies and external clocks are not cut off in this config (no support for System OFF in l-o), so the HW latencies are lower than expected. The HW measurements need to be performed as soon as l-o supports the System OFF. The measurements from TI are used for the real HW latency.

Here are some scope screenshots showing the time delta between the wake-up event (USER button press, trace A) and the end of omap_sram_idle (USR1 Led).

For RET mode, showing a delta of 408us:

Scope capture ret.jpg

For OFF mode, showing a delta of 2700us:

Scope capture off.jpg

GPT tracer

Since GPT12 is used as a wake-up source from the idle mode, it can be used to track the timings during the wake-up sequence. A patch is needed to let the timer count after it overflowed and woke up the system.

The GPT runs on 32KHz clock and so the resolution is limited to 30.518us. Given the latencies to measure for OFF mode, the resolution is accpetable.

4 GPT measurements are performed during the wake-up:

SW trace usage

Enable the power events and dump the trace:

# echo 1 > /debug/tracing/events/power/enable
# cat /debug/tracing/trace_pipe &

Enable the system idle in RET mode:

# echo 5 > /sys/devices/platform/omap/omap-hsuart.0/sleep_timeout 
# echo 5 > /sys/devices/platform/omap/omap-hsuart.1/sleep_timeout 
# echo 5 > /sys/devices/platform/omap/omap-hsuart.2/sleep_timeout 

# echo 0 > /debug/pm_debug/enable_off_mode
# echo 1 > /debug/pm_debug/sleep_while_idle

Trace output:

[   62.311462] *** GPT12 wake-up (HW wake-up, ASM restore, delta trace1-7): 183, 0, 244 us       => Dump of GPT timing deltas
          <idle>-0     [000]    62.241608: power_start: type=1 state=1 cpu_id=0                  => Idle start
          <idle>-0     [000]    62.241608: power_start: type=4 state=1 cpu_id=0                  => First suspend SW trace in omap_sram_idle
          <idle>-0     [000]    62.241638: power_start: type=4 state=2 cpu_id=0                  => ...
          <idle>-0     [000]    62.241669: power_start: type=4 state=3 cpu_id=0
          <idle>-0     [000]    62.241699: power_domain_target: name=neon_pwrdm state=1 cpu_id=0
          <idle>-0     [000]    62.241699: power_start: type=4 state=4 cpu_id=0
          <idle>-0     [000]    62.241699: clock_disable: name=uart3_fck state=0 cpu_id=0
          <idle>-0     [000]    62.241730: power_start: type=4 state=5 cpu_id=0
          <idle>-0     [000]    62.241730: clock_disable: name=uart1_fck state=0 cpu_id=0
          <idle>-0     [000]    62.241730: clock_disable: name=uart2_fck state=0 cpu_id=0
          <idle>-0     [000]    62.241760: power_start: type=4 state=6 cpu_id=0
          <idle>-0     [000]    62.241760: power_start: type=4 state=7 cpu_id=0
          <idle>-0     [000]    62.241760: power_start: type=4 state=8 cpu_id=0                  => Last suspend SW trace in omap_sram_idle
          <idle>-0     [000]    62.311188: power_start: type=5 state=1 cpu_id=0                  => First resume SW trace in omap_sram_idle
          <idle>-0     [000]    62.311188: power_start: type=5 state=2 cpu_id=0                  => ...
          <idle>-0     [000]    62.311188: power_start: type=5 state=3 cpu_id=0
          <idle>-0     [000]    62.311188: power_start: type=5 state=4 cpu_id=0
          <idle>-0     [000]    62.311218: clock_enable: name=uart1_fck state=1 cpu_id=0
          <idle>-0     [000]    62.311310: clock_enable: name=uart2_fck state=1 cpu_id=0
          <idle>-0     [000]    62.311310: power_start: type=5 state=5 cpu_id=0
          <idle>-0     [000]    62.311340: clock_enable: name=uart3_fck state=1 cpu_id=0
          <idle>-0     [000]    62.311340: power_start: type=5 state=6 cpu_id=0
          <idle>-0     [000]    62.311432: power_start: type=5 state=7 cpu_id=0                  => Last resume SW trace in omap_sram_idle
          <idle>-0     [000]    62.311462: power_end: cpu_id=0                                   => Idle end

Enable the system idle in OFF mode:

# echo 5 > /sys/devices/platform/omap/omap-hsuart.0/sleep_timeout 
# echo 5 > /sys/devices/platform/omap/omap-hsuart.1/sleep_timeout 
# echo 5 > /sys/devices/platform/omap/omap-hsuart.2/sleep_timeout 

# echo 1 > /debug/pm_debug/enable_off_mode
# echo 1 > /debug/pm_debug/sleep_while_idle

Trace output:

/ # echo 1 > /debug/pm_debug/enable_off_mode
/ #           
              sh-503   [000]    70.862366: power_domain_target: name=iva2_pwrdm state=0 cpu_id=0
              sh-503   [000]    70.862396: power_domain_target: name=mpu_pwrdm state=0 cpu_id=0
              sh-503   [000]    70.862396: power_domain_target: name=neon_pwrdm state=0 cpu_id=0
              sh-503   [000]    70.862396: power_domain_target: name=core_pwrdm state=0 cpu_id=0
              sh-503   [000]    70.862427: power_domain_target: name=cam_pwrdm state=0 cpu_id=0
              sh-503   [000]    70.862457: power_domain_target: name=dss_pwrdm state=0 cpu_id=0
              sh-503   [000]    70.862488: power_domain_target: name=per_pwrdm state=0 cpu_id=0
              sh-503   [000]    70.862488: power_domain_target: name=usbhost_pwrdm state=0 cpu_id=0
/ # 
[  557.240020] *** GPT12 wake-up (HW wake-up, ASM restore, delta trace1-7): 1495, 915, 488 us    => Dump of GPT timing deltas
          <idle>-0     [000]   557.156769: power_start: type=1 state=1 cpu_id=0                  => Idle start
          <idle>-0     [000]   557.156769: power_start: type=4 state=1 cpu_id=0                  => First suspend SW trace in omap_sram_idle
          <idle>-0     [000]   557.156769: power_start: type=4 state=2 cpu_id=0                  => ...
          <idle>-0     [000]   557.156830: power_start: type=4 state=3 cpu_id=0
          <idle>-0     [000]   557.156830: power_domain_target: name=neon_pwrdm state=0 cpu_id=0
          <idle>-0     [000]   557.156830: power_start: type=4 state=4 cpu_id=0
          <idle>-0     [000]   557.156860: clock_disable: name=uart3_fck state=0 cpu_id=0
          <idle>-0     [000]   557.156891: power_start: type=4 state=5 cpu_id=0
          <idle>-0     [000]   557.156891: clock_disable: name=uart1_fck state=0 cpu_id=0
          <idle>-0     [000]   557.156921: clock_disable: name=uart2_fck state=0 cpu_id=0
          <idle>-0     [000]   557.157013: power_start: type=4 state=6 cpu_id=0
          <idle>-0     [000]   557.157013: power_start: type=4 state=7 cpu_id=0
          <idle>-0     [000]   557.157898: power_start: type=4 state=8 cpu_id=0                  => Last suspend SW trace in omap_sram_idle
          <idle>-0     [000]   557.236084: power_start: type=5 state=1 cpu_id=0                  => First resume SW trace in omap_sram_idle
          <idle>-0     [000]   557.236145: power_start: type=5 state=2 cpu_id=0                  => ...
          <idle>-0     [000]   557.236206: power_start: type=5 state=3 cpu_id=0
          <idle>-0     [000]   557.236267: power_start: type=5 state=4 cpu_id=0
          <idle>-0     [000]   557.236389: clock_enable: name=uart1_fck state=1 cpu_id=0
          <idle>-0     [000]   557.236450: clock_enable: name=uart2_fck state=1 cpu_id=0
          <idle>-0     [000]   557.236450: power_start: type=5 state=5 cpu_id=0
          <idle>-0     [000]   557.236481: clock_enable: name=uart3_fck state=1 cpu_id=0
          <idle>-0     [000]   557.236511: power_start: type=5 state=6 cpu_id=0
          <idle>-0     [000]   557.236572: power_start: type=5 state=7 cpu_id=0                  => Last resume SW trace in omap_sram_idle
          <idle>-0     [000]   557.236602: power_end: cpu_id=0                                   => Idle end

Results interpretation

The low power transition sequence is pictured as nested calls to functions:

Low power transition sequence.png

The measured results (from the HW and SW traces) are mapped to the pictured states according to the following table:

Pictured state Trace point Performed SW action
Idle enter start suspend System ready to enter idle
omap_sram_idle 1 suspend trace point 1 Enter omap_sram_idle
omap_sram_idle 2 suspend trace point 2 calculation of next power domains modes
omap_sram_idle 3 suspend trace point 3 Power domains pre-transition: program power domains current state, clear status
omap_sram_idle 4 suspend trace point 4 Context save for NEON
IO pad and chain new state programmed
omap_sram_idle 5 suspend trace point 5 Context save for PER, GPIO
Prepare UARTs 2&3
omap_sram_idle 6 suspend trace point 6 Context save for CORE and PRCM
Prepare UARTs 0&1
omap_sram_idle 7 suspend trace point 7 Context save for INTC
Program SDRC
WFI enter suspend trace point 8 GPIO HW trace
MPU context save in ASM (caches, registers, disable cache & prediction)
System OFF active - sys_off_mode, external clocks and power supplies to be measured with System OFF support -
Wake-up event: IO or GPT12 HW trace A (if IO wake-up)
GPT12=0 (if GPT wake-up)
-
System OFF inactive - sys_off_mode, external clocks and power supplies to be measured with System OFF support -
WFI exit GPT12 sampling right after WFI -
omap_sram_idle 1 GPT12 sampling at return from ASM code
Wake-up trace point 1
SDRC errata for ES3.1
MPU context restore
MMU restore and enable
omap_sram_idle 2 wake-up trace point 2 cpu_init
omap_sram_idle 3 wake-up trace point 3 SDRC settings restore
omap_sram_idle 4 wake-up trace point 4 Restore MMU tables
Enable caches and prediction
omap_sram_idle 5 wake-up trace point 5 Context restore for CORE, PRCM, SRAM, SMS
Resume UARTs 0&1
omap_sram_idle 6 wake-up trace point 6 Context restore for PER, INTC, GPIO
IO pad & chain
Resume UARTS 2&3
omap_sram_idle 7 wake-up trace point 7
GPT sampling
HW trace B
Power domains post-transition: program power domains current state, clear status
Restore SDRC settings
Idle exit exit suspend System out of idle

Results

PSI measurements results

Some timings measurements have been made by the TI PSI team. The following tables gives the results for the sleep and wake-up latencies for the C-states:

C states sleep latency.png
C states wake up latency.png

Note: in the linux code there is no C7/C8/C9 as in the table. C7 is MPU OFF + CORE OFF, which is identical to C9 in the table.

A model with the energy spent in the C-states has been built from the measured numbers. Here is the graph of the energy vs time:

C states os idle energy.png

Taking the minimum energy from the graph allows to identify the 4 energy-wise interesting C-states: C1, C3, C5, C9 and the threshold time for those C-states to be efficient:

C states data.png

Notes:

HW and SW measurements results

Here are the results for full RET and full OFF modes:

Sequence Time (us) - RET = C5 Time (us) - OFF = C9
From idle start till omap_sram_idle entry 0 0
From omap_sram_idle entry till WFI 152 1129
... HW sleep...
From WKUP event till WFI
(HW wake-up - GPT12)
183 1495
From WFI till return from omap34xx_save_cpu_context_wfi
(MPU context restore in ASM)
0 915
From return from omap34xx_save_cpu_context_wfi till end of omap_sram_idle
(System restore)
244 488
From end of omap_sram_idle till return from idle 30 30

Aggregated timings results

From the various sources of data the following figures are used:

Links

Device latency patches

PM QoS device constraint code patches

T2 scripts information page

Attachments

Kernel patches and config

File:OMAP latency measurements patches and config.tar.gz

--Jpihet 12 November 2010

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