[PATCH 2/4] arm: dts: exynos: add exynos5420 cpu capacity-dmips-mhz information
From: dietmar.eggemann@arm.com (Dietmar Eggemann)
Date: 2017-08-31 10:36:13
Also in:
linux-devicetree, linux-renesas-soc, linux-samsung-soc, lkml
On 30/08/17 21:26, Krzysztof Kozlowski wrote:
On Wed, Aug 30, 2017 at 03:41:18PM +0100, Dietmar Eggemann wrote:quoted
The following 'capacity-dmips-mhz' dt property values are used: Cortex-A15: 1024, Cortex-A7: 539 They have been derived from the cpu_efficiency values: Cortex-A15: 3891, Cortex-A7: 2048 by scaling them so that the Cortex-A15s (big cores) use 1024. The cpu_efficiency values were originally derived from the "Big.LITTLE Processing with ARM Cortex?-A15 & Cortex-A7" white paper (http://www.cl.cam.ac.uk/~rdm34/big.LITTLE.pdf). Table 1 lists 1.9x (3891/2048) as the Cortex-A15 vs Cortex-A7 performance ratio for the Dhrystone benchmark. The following platforms are affected once cpu-invariant accounting support is re-connected to the task scheduler: arndale-octa, peach-pi, peach-pit, smdk5420 The patch has been tested on Samsung Chromebook 2 13" (peach-pi, Exynos 5800). $ cat /sys/devices/system/cpu/cpu*/cpu_capacity 1024 1024 1024 1024 389 389 389 389I am missing something... shouldn't this be 539? Or is it scaled with the clock-frequency (1 GHz) value?
Yeah, the capacity-dmips-mhz dt value of 539 for the little cpus is scaled by 1.3/1.8 (max cpu capacity/ system wide max cpu capacity): 539 * 1.3/1.8 = 389 This max cpu capacity scaling is part of both solutions, the 'cpu capacity-dmips-mhz' and the 'cpu_efficiency/clock-frequency dt property' one. The (original*) cpu capacity on a heterogeneous platform expresses uArch and max cpu frequency differences between the (logical) cpus of the system. * not further reduced by rt and/or irq pressure. [...]