Re: New fast(?)-boot results on ARM
Linus Walleij wrote: 2009/8/14 Robert Schwebel : On Fri, Aug 14, 2009 at 12:19:48PM -0600, Zan Lynx wrote: That's factor 70 away from the 110 ms boot time Tim has talked about some days ago (and he measured on an ARM cpu which had almost half the speed of this one), and I'm wondering what we can do to improve the boot time. 2.4s in uncompression? That seems like an obvious target for improvement. Indeed, we'll check that. We got rid of uncompression on a flash-based system vastly improving boot time. The reason is that compressed kernels are faster only when the throughput to the persistent storage is lower than the decompression throughput, and on typical embedded systems with DMA the throughput to memory outperforms the CPU-based decompression. I thought of another thing to check related to slow decompression. If the kernel, bootloader or hardware is in charge of setting CPU power and speed scaling, then you should check that it boots with the CPU set at maximum speed instead of slowest. -- Zan Lynx zl...@acm.org "Knowledge is Power. Power Corrupts. Study Hard. Be Evil." -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: New fast(?)-boot results on ARM
Robert Schwebel wrote: - 2.4 s up from u-boot to the end of "Uncompressing Linux" - 300 ms until ubifs initialization starts - 3.7 s for ubifs, until "mounted root" So we basically have 7 s for the kernel. The rest is userspace, which hasn't seen much optimization yet, other than trying to start the GUI application as early as possible, while doing all other init stuff in parallel. Adding "quiet" brings us another 300 ms. That's factor 70 away from the 110 ms boot time Tim has talked about some days ago (and he measured on an ARM cpu which had almost half the speed of this one), and I'm wondering what we can do to improve the boot time. 2.4s in uncompression? That seems like an obvious target for improvement. Your kernel seems awfully large. 3104K code? You should definitely find out what is making it that big and cut out everything you do not need. You might even try some of the embedded system scripts that rip out all the printk strings. If you get the kernel size way down then use a uncompressed kernel and it should boot a lot faster if the bottleneck is CPU speed. However, it is probably IO speed. There could be something really wrong and slow with your MTD. Does it DMA or is it doing something crazy like using the CPU to read a byte at a time? Or maybe its cheap and slow flash. In that case I think your only hope is to make all the code as small as possible and/or find a different flash filesystem that does not have to read so much of the device to mount. Perhaps use a read-only compressed filesystem for the system binaries and reflash it for software upgrades. Only init and mount the writable flash for user-storable data well after system boot has finished. -- Zan Lynx zl...@acm.org "Knowledge is Power. Power Corrupts. Study Hard. Be Evil." -- To unsubscribe from this list: send the line "unsubscribe linux-embedded" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
