[RFC PATCH 0/11] ARM: cpu topology Cortex-A9

[Amit Kucheria]

Vincent,

What is the status of this after talks with the scheduler maintainers
in Prague last week? Have you shared this with Peter Z et al.

Regards,
Amit

On Fri, Oct 21, 2011 at 12:52 PM, Vincent Guittot
<vincent.guittot at linaro.org> wrote:
> The sched_mc feature has been originally designed to improve power
> consumption of multi-package system and several architecture functions
> are available to tune the topology and the scheduler's parameters when
> scheduler rebuilds the sched_domain hierarchy (change the
> sched_mc_power_savings level). This patches series is a trial to
> improve the power consumption of dual and quad cortex-A9 when the
> sched_mc_power_savings is set to 2. The following patch's policy is to
> accept up to 4 threads (can be configured) in the run queue of a core
> before starting to load balance if cpu runs at low frequencies but to
> accept only 1 thread for high frequencies, which is the normal
> behaviour. The goal is to use only one cpu in light load situation and
> both cpu in heavy load situation
>
> Patches [1-3]  modify the ARM cpu topology according to
> sched_mc_power_savings value and Cortex id
> Patch [4] enables ARCH_POWER feature of the scheduler
> Patch [5] adds  ARCH_POWER function for ARM platform
> Patches [6-7] modify the cpu_power of CA-9 according to
> sched_mc_power_savings' level and current frequency. The main goal is
> to increase the capacity of a core when using low cpu frequency in
> order to pull tasks on this core. Note that this behaviour is not
> really advised but it can be seen as an intermediate step between the
> use of cpu hotplug (which is not a power saving feature) and a new
> load balancer which will take into account low load situation on dual
> core.
> Patch [8] ensures that cpu0 is used in priority when only one CPU is running
> Patch [9] adds some debugfs interface for test purpose
> Patch [10] ensures that the cpu_power will be update periodically
> Patch [11] fixes an issue around the trigger of ilb.
>
> TODO list:
> -remove useless start of ilb when the core has capacity.
> -add a method (DT, sysfs, ...) to set threshold for using 1 or 2 cpus
> for dual CA-9
> -irq balancing
>
> The tests hereafter have been done on a u8500 with kernel linaro-3.1.
> They check that there is no obvious lost of performance when
> sched_mc=2.
>
> sysbench --test=cpu --num-threads=12 --max-time=20 run
> Test execution summary:    sched_mc=0   sched_mc=2    cpu hotplug
>    total number of events:               665               664
>        336
>    per-request statistics:
>         min:                             92.68ms         70.53ms       618.89ms
>         avg:                           361.75ms        361.38ms       725.29ms
>         max:                          421.08ms        420.73ms       840.74ms
>         approx.  95 percentile: 402.28ms         390.53ms      760.17ms
>
> sysbench --test=threads --thread-locks=9 --num-threads=12 --max-time=20 run
> Test execution summary:    sched_mc=0   sched_mc=2    cpu hotplug
>    total number of events:           10000            10000              3129
>    per-request statistics:
>         min:                               1.62ms          1.70ms
>    13.16ms
>         avg:                              22.23ms        21.87ms
>   76.77ms
>         max:                           153.52ms      133.99ms        173.82ms
>         approx.  95 percentile:    54.12ms        52.65ms        136.32ms
>
> sysbench --test=threads --thread-locks=2 --num-threads=3 --max-time=20 run
> Test execution summary:    sched_mc=0   sched_mc=2    cpu hotplug
>    total number of events:           10000            10000            10000
>    per-request statistics:
>         min:                               1.38ms          1.38ms
>     5.70ms
>         avg:                               4.67ms          5.37ms
>    11.85ms
>         max:                            36.84ms         32.42ms        32.58ms
>         approx.  95 percentile:    14.34ms        12.89ms        21.30ms
>
> cyclictest -q -t -D 20
> Only one cpu is used during this test when sched_mc=2 whereas both cpu
> are used when sched_mc=0
> Test execution summary:    sched_mc=0   sched_mc=2    cpu hotplug
>
>                        Avg, Max:       15, 434         19, 2145        17, 3556
>                        Avg, Max:       14, 104         19, 1686        17, 3593
>
> Regards,
> Vincent
>
> _______________________________________________
> linaro-dev mailing list
> linaro-dev at lists.linaro.org
> http://lists.linaro.org/mailman/listinfo/linaro-dev
>