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SubjectRe: HPET regression in 2.6.26 versus 2.6.25 -- revert for 2.6.26-rc1 failed
Hi David,

On Wed, 13 Aug 2008, David Witbrodt wrote:

> [Yinghai, please note that I did not request a patch to revert the
> problem commit. I was merely experimenting -- on my own time, so
> you folks would not have to bother -- to see if I could make it
> work. I should have made that more clear! Having said that, I am
> glad to test changes of any kind on my machine: reverts, code for
> debugging or info, experiments, etc.]

I'm not sure Yinghai's revert patch is completely equivalent to
a revert of the original problematic commit, by a side-by-side
comparison of the original commit with his recent revert patch,
but then I don't really know that code at all.

In the original code there was a section (in e820_reserve_resources()):

#ifdef CONFIG_KEXEC
if (crashk_res.start != crashk_res.end)
request_resource(res, &crashk_res);
#endif
If you don't have CONFIG_KEXEC defined in your .config, which is
probably the case, then you would never request a crashk_res resource.
But in the code after the original commit, it unconditionally calls
(in reserve_crashkernel()):

crashk_res.start = crash_base;
crashk_res.end = crash_base + crash_size - 1;
insert_resource(&iomem_resource, &crashk_res);

And after Yinghai's revert patch it still does (in reserve_crashkernel()):

crashk_res.start = crash_base;
crashk_res.end = crash_base + crash_size - 1;
crashk_res_ptr = &crashk_res;

and (in setup_arch()):

num_res = 3;
if (crashk_res_ptr) {
res_kernel[num_res] = crashk_res_ptr;
num_res++;
}
e820_reserve_resources(res_kernel, num_res);
then (in e820_reserve_resources()):

for (j = 0; j < nr_res_k; j++) {
if (!res_kernel[j])
continue;
request_resource(res, res_kernel[j]);
}
which for j == 3 is:

request_resource(res, &crashk_res);

Now it would appear that the new:

insert_resource(&iomem_resource, &crashk_res);

or new:

request_resource(res, &crashk_res);

should be noops. But if for any reason crash_size is not zero,
then there could be a difference. I have no idea if this is at all
significant, but I thought I'd point it out just in case.

-Bill


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