Messages in this thread | | | Subject | Re: [RFT][Update][PATCH v2 2/2] PM / QoS: Fix device resume latency framework | From | Reinette Chatre <> | Date | Mon, 6 Nov 2017 09:47:35 -0800 |
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Hi Rafael,
On 11/4/2017 5:34 AM, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > The special value of 0 for device resume latency PM QoS means > "no restriction", but there are two problems with that. > > First, device resume latency PM QoS requests with 0 as the > value are always put in front of requests with positive > values in the priority lists used internally by the PM QoS > framework, causing 0 to be chosen as an effective constraint > value. However, that 0 is then interpreted as "no restriction" > effectively overriding the other requests with specific > restrictions which is incorrect. > > Second, the users of device resume latency PM QoS have no > way to specify that *any* resume latency at all should be > avoided, which is an artificial limitation in general. > > To address these issues, modify device resume latency PM QoS to > use S32_MAX as the "no constraint" value and 0 as the "no > latency at all" one and rework its users (the cpuidle menu > governor, the genpd QoS governor and the runtime PM framework) > to follow these changes. > > Also add a special "n/a" value to the corresponding user space I/F > to allow user space to indicate that it cannot accept any resume > latencies at all for the given device. > > Fixes: 85dc0b8a4019 (PM / QoS: Make it possible to expose PM QoS latency constraints) > Link: https://bugzilla.kernel.org/show_bug.cgi?id=197323 > Reported-by: Reinette Chatre <reinette.chatre@intel.com> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > Acked-by: Ramesh Thomas <ramesh.thomas@intel.com> > --- > > Re-sending as an update rather than as v3, because the update is very minor > (an additional check under the WARN_ON() in apply_constraint()). > > Reinette, please test this one instead of the last version. The WARN_ON() > issue should be gone with this. >
I tested this update of the v2 2/2 patch with v2 of 1/2 but please note as captured below that I am testing with the menu governor, so not testing 1/2 if I understand correctly.
I just repeated the test I ran against the original patch that was merged, with some details added. I hope that it has some value to you considering that it did not catch all issues the first time :(
I tested on an Intel(R) NUC NUC6CAYS (Apollo Lake with a Goldmont cpu). As you maybe know it has some issues with monitor/mwait, so acpi_idle is used: # grep . /sys/devices/system/cpu/cpuidle/current_* /sys/devices/system/cpu/cpuidle/current_driver:acpi_idle /sys/devices/system/cpu/cpuidle/current_governor_ro:menu
As with your original patch I still see the new behavior on boot: swapper/0-1 [000] .... 0.347284: dev_pm_qos_add_request: device=cpu0 type=DEV_PM_QOS_RESUME_LATENCY new_value=2147483647 swapper/0-1 [000] .... 0.347300: pm_qos_update_target: action=ADD_REQ prev_value=2147483647 curr_value=2147483647 swapper/0-1 [000] .... 0.347533: dev_pm_qos_add_request: device=cpu1 type=DEV_PM_QOS_RESUME_LATENCY new_value=2147483647 swapper/0-1 [000] .... 0.347536: pm_qos_update_target: action=ADD_REQ prev_value=2147483647 curr_value=2147483647 swapper/0-1 [000] .... 0.347741: dev_pm_qos_add_request: device=cpu2 type=DEV_PM_QOS_RESUME_LATENCY new_value=2147483647 swapper/0-1 [000] .... 0.347743: pm_qos_update_target: action=ADD_REQ prev_value=2147483647 curr_value=2147483647 swapper/0-1 [000] .... 0.347958: dev_pm_qos_add_request: device=cpu3 type=DEV_PM_QOS_RESUME_LATENCY new_value=2147483647 swapper/0-1 [000] .... 0.347961: pm_qos_update_target: action=ADD_REQ prev_value=2147483647 curr_value=2147483647
Even though the default latency required values on boot are much higher, the user API still shows zero: # grep . /sys/devices/system/cpu/cpu?/power/pm_qos_resume_latency_us /sys/devices/system/cpu/cpu0/power/pm_qos_resume_latency_us:0 /sys/devices/system/cpu/cpu1/power/pm_qos_resume_latency_us:0 /sys/devices/system/cpu/cpu2/power/pm_qos_resume_latency_us:0 /sys/devices/system/cpu/cpu3/power/pm_qos_resume_latency_us:0
At this time when I run turbostat I observe that more than 99% of time is spent in C6 as reported by the actual hardware counters (the CPU%c6 value). I also see that the requested value is more than 99% for C3.
In my code the dev_pm_qos_add_request() API is used to request a new latency requirement of 30 usec (this previously failed) from core #2 and #3. I run my code with tracing enabled while also running turbostat. Tracing now shows me a successful request:
runit-505 [003] .... 393.656679: dev_pm_qos_add_request: device=cpu2 type=DEV_PM_QOS_RESUME_LATENCY new_value=30 runit-505 [003] .... 393.656700: pm_qos_update_target: action=ADD_REQ prev_value=2147483647 curr_value=30 runit-505 [003] .... 393.656705: dev_pm_qos_add_request: device=cpu3 type=DEV_PM_QOS_RESUME_LATENCY new_value=30 runit-505 [003] .... 393.656707: pm_qos_update_target: action=ADD_REQ prev_value=2147483647 curr_value=30
Turbostat also reflects this with cores 2 and 3 now reporting more than 99% in their CPU%c1 and C1% columns.
User API still shows: # grep . /sys/devices/system/cpu/cpu?/power/pm_qos_resume_latency_us /sys/devices/system/cpu/cpu0/power/pm_qos_resume_latency_us:0 /sys/devices/system/cpu/cpu1/power/pm_qos_resume_latency_us:0 /sys/devices/system/cpu/cpu2/power/pm_qos_resume_latency_us:0 /sys/devices/system/cpu/cpu3/power/pm_qos_resume_latency_us:0
Next I use dev_pm_qos_remove_request() to remove the previous latency requirement (again with tracing and turbostat running).
rmdir-665 [002] .... 686.925230: dev_pm_qos_remove_request: device=cpu3 type=DEV_PM_QOS_RESUME_LATENCY new_value=-1 rmdir-665 [002] .... 686.925250: pm_qos_update_target: action=REMOVE_REQ prev_value=30 curr_value=2147483647 rmdir-665 [002] .... 686.925254: dev_pm_qos_remove_request: device=cpu2 type=DEV_PM_QOS_RESUME_LATENCY new_value=-1 rmdir-665 [002] .... 686.925257: pm_qos_update_target: action=REMOVE_REQ prev_value=30 curr_value=2147483647
Turbostat also shows that cores 2 and 3 return to their high residency in C6.
As before, user API shows: # grep . /sys/devices/system/cpu/cpu?/power/pm_qos_resume_latency_us /sys/devices/system/cpu/cpu0/power/pm_qos_resume_latency_us:0 /sys/devices/system/cpu/cpu1/power/pm_qos_resume_latency_us:0 /sys/devices/system/cpu/cpu2/power/pm_qos_resume_latency_us:0 /sys/devices/system/cpu/cpu3/power/pm_qos_resume_latency_us:0
Thank you very much for making this work!
Tested-by: Reinette Chatre <reinette.chatre@intel.com>
Reinette
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