Vivek Goyal <[EMAIL PROTECTED]> writes: > On Tue, Aug 01, 2006 at 04:58:49AM -0600, Eric W. Biederman wrote: >> >> The problem: >> >> We can't always run the kernel at 1MB or 2MB, and so people who need >> different addresses must build multiple kernels. The bzImage format >> can't even represent loading a kernel at other than it's default address. >> With kexec on panic now starting to be used by distros having a kernel >> not running at the default load address is starting to become common. >> > Hi Eric, > > There seems to be a small anomaly in the current set of patches for i386. > > For example if one compiles the kernel with CONFIG_RELOCATABLE=y > and CONFIG_PHYSICAL_START=0x400000 (4MB) and he uses grub to load > the kernel then kernel would run from 1MB location. I think user would > expect it to run from 4MB location.
Agreed. That is a non-intuitive, and should probably be fixed. > I think distro's might want to keep above config options enabled. > CONFIG_RELOCATABLE=y so that kexec can load kdump kernel at a > different address and CONFIG_PHYSICAL_START=non 1MB location, to > extract better performance. (As we had discussions on mailing list > some time back.) > > In principle this is a limitation on boot-loaders part but as we can > not fix the boot-loaders out there, probably we can try fixing it > at kernel level. > > What I have done here is that decompressor code will determine the > final resting place of the kernel based on boot loader type. So > if I have been loaded by kexec, I am supposed to run from loaded address > otherwise I am supposed to run from CONFIG_PHYSICAL_START as I have been > loaded at 1MB address due to boot loader limitation and that's not the > intention. > > A prototype patch is attached with the mail. I have assumed that I can > assign a boot loader type id 9 to kexec (Documentation/i386/boot.txt). > Also assuming that all other boot loaders apart from kexec have got 1MB > limitation. If not, its trivial to include their boot loader ids also. > > I have tested this patch and it works fine. What do you think about > this approach ? I think there is some value in it. But I need to digest it. I have a cold right now and am running pretty weak, so it is going to take me a little bit to look at this. I don't like taking action based upon bootloader type. As that assumes all kinds of things. But having better rules for when we perform relocation makes sense. There might be a way to detect coming from setup.S I gave it some care last time, I worked through this and it didn't quite work. I guess the practical question is do people see a real performance benefit when loading the kernel at 4MB? Possibly the right solution is to do like I did on x86_64 and simply remove CONFIG_PHYSICAL_START, and always place the kernel at 4MB, or something like that. The practical question is what to do to keep the complexity from spinning out of control. Removing CONFIG_PHYSICAL_START would seriously help with that. Eric _______________________________________________ fastboot mailing list [email protected] https://lists.osdl.org/mailman/listinfo/fastboot
