On Feb 8, 2012, at 8:55 AM, Dmitry Antipov wrote: > On 02/08/2012 01:32 AM, Andrew Richardson wrote: > >> Do you recommend using "Get linaro image tools: method 2 (source code)" >> ( http://releases.linaro.org/12.01/ubuntu/leb-panda/ ) and building the >> kernel myself? > > Unfortunately this is the only way. In theory, there are clocksource= > boot option, and sysfs interface under /sys/devices/system/clocksource, > but, IIUC, there is no way to compile the kernel with both 32K and MPU > timers support and then select one of them for the default clock source > at the boot time or when the system is running. > >> It seems to me that we would want to disable some of the power-saving >> changes that have been made, such as this timer, and possibly configure >> other settings like cache behavior, though I have no idea >> how they're currently set. I have a bunch of docs from ARM on power and >> cache config, but I haven't messed around with them as I'm not sure where >> to start. My best guess is that I would have to rebuild the kernel to >> start handling that configuration myself. Is that true? > > If you're seriously concerned on the optimization for the particular > workload, you definitely should. > >> Some people ( http://groups.google.com/group/pandaboard/browse_thread/thread/a18fa3514d130720 ) >> have mentioned enabling line fill and prefetching to speed up memcpy >> operations, which also seems useful. Is this also a kernel-level setting? > > Sure. Caching (and it's relationship to real memory speed) is a hard topic. > For the starting point, try: > > 1. Read http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka13544.html > (this is for A8, but should be more or less applicable to A9); > > 2. Run 'dmesg | grep -i cache' and check for the something similar to: > > L310 cache controller enabled > l2x0: 16 ways, CACHE_ID 0x410000c4, AUX_CTRL 0x7e470000, Cache size: 1048576 B > > 3. Read http://infocenter.arm.com/help/topic/com.arm.doc.ddi0246f/DDI0246F_l2c310_r3p2_trm.pdf > and realize the meaning of these AUX_CTRL bits; > > 4. Read arch/arm/mach-omap2/omap4-common.c and arch/arm/mm/cache-l2x0.c, try to play > with 'aux_ctrl' bits within omap_l2_cache_init() and check whether it affects your > workload. Note this may cause kernel crash and/or prevent the system from booting at all. > > Dmitry > > -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
