On 12 January 2015 at 10:23, Krzysztof Kozlowski <k.kozlowski@xxxxxxxxxxx> wrote: > Hi, > > > I would like to hear some comments about idea of scaling MMC clock > frequency. The basic idea is to lower the clock when device is > completely idle or not busy enough. > > The patchset adds MMC card as a devfreq device and uses simple_ondemand > as governor. In idle this gave benefits (less energy consumed during > idle): > 1. Trats2 (Exynos4412): 2.6% > 2. Rinato (Exynos3250): 1% > > but (especially on Rinato) it had impact on performance (probably > because ondemand triggering a little to late). What is interesting > manually changing the clock (without this patchset) gave slightly > bigger benefits. Maybe the devfreq introduces noticeable overhead? Could it be because of the polling interval being too long thus it being too slow to ramp up? That's a problem with all polling devfreq drivers, it has been proposed before using pm_qos to to reduce the polling interval when some event indicates that the utilization may grow abruptly in the near future. I don't think pm_qos is the best mechanism for that, maybe something new needs to be devised. Regards, Tomeu > > Comments are welcomed. Maybe on other platforms this has bigger impact? > > Best regards, > Krzysztof > > > Krzysztof Kozlowski (3): > mmc: Add dynamic frequency scaling > ARM: dts: Specify MSHC realistic clocks and use frequency scaling > ARM: dts: Use frequency scaling for MSHC > > Documentation/devicetree/bindings/mmc/mmc.txt | 2 + > arch/arm/boot/dts/exynos3250-rinato.dts | 1 + > arch/arm/boot/dts/exynos4412-trats2.dts | 4 +- > drivers/mmc/card/block.c | 247 ++++++++++++++++++++++++++ > drivers/mmc/core/Kconfig | 16 ++ > drivers/mmc/core/core.h | 1 - > drivers/mmc/core/host.c | 2 + > include/linux/mmc/card.h | 8 + > include/linux/mmc/host.h | 3 + > 9 files changed, 282 insertions(+), 2 deletions(-) > > -- > 1.9.1 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
