Robert Schwebel wrote: > On Fri, Jul 31, 2009 at 12:48:37PM -0700, Tim Bird wrote: >>> Those fractions-of-seconds boot times are beyond the reach of the >>> 200 MHz-class ARM9 processors and similar, where it takes two or >>> three seconds just to load and uncompress the kernel from NOR or >>> NAND flash. >> While I don't disagree from a practical standpoint - at Sony using XIP >> we have been able to finish kernel boot on a 192 MHZ ARM9 in 186 >> milliseconds. In the lab, anyway? > > Wow, that's pretty fast; if that would be possible for standard > scenarios, it would indeed be better to do everything on the kernel > side. > > Can you elaborate about the details of that experiment? Was that normal > XIP from NOR? What size has this kernel been? This was done quite some time ago, and it looks like my memory was not too good. According to slides I did at the time, it was actually 110 milliseconds. I'm sure this was a 2.4 kernel (likely 2.4.20). I couldn't find the size of the kernel used in the test, but I think it was about 800k, uncompressed. (I'm not positive, though.) It was normal XIP from NOR flash. See slides 21 and 22 in the following: http://elinux.org/images/7/78/ReducingStartupTime_v0.8.pdf Here is some salient data: With Compression W/ O Compression XIP Copy 56 msec 120 msec 0 msec Decompression 545 msec 0 msec 0 msec Kernel execution 88 msec 88 msec 110 msec Total: 689 msec 208 msec 110 msec Note that copy time went up when going from a compressed to an uncompressed kernel. Decompression time went down (to 0, no surpise). When XIP was used, both copy time and decompression time were eliminated, but kernel execution time for the boot went from 88 msec to 110 msec. So XIP did incur a pretty hefty runtime penalty. Aaahhh, 2.4. The kernel was simpler in those days... :-) -- Tim ============================= Tim Bird Architecture Group Chair, CE Linux Forum Senior Staff Engineer, Sony Corporation of America ============================= -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
