[PATCH v2 0/2] arm64: Cut rebuild time when changing CONFIG_BLK_DEV_INITRD

Florian Fainelli f.fainelli at gmail.com
Thu Oct 25 16:07:13 PDT 2018


On 10/25/18 2:13 PM, Rob Herring wrote:
> On Thu, Oct 25, 2018 at 12:30 PM Mike Rapoport <rppt at linux.ibm.com> wrote:
>>
>> On Thu, Oct 25, 2018 at 08:15:15AM -0500, Rob Herring wrote:
>>> +Ard
>>>
>>> On Thu, Oct 25, 2018 at 4:38 AM Mike Rapoport <rppt at linux.ibm.com> wrote:
>>>>
>>>> On Wed, Oct 24, 2018 at 02:55:17PM -0500, Rob Herring wrote:
>>>>> On Wed, Oct 24, 2018 at 2:33 PM Florian Fainelli <f.fainelli at gmail.com> wrote:
>>>>>>
>>>>>> Hi all,
>>>>>>
>>>>>> While investigating why ARM64 required a ton of objects to be rebuilt
>>>>>> when toggling CONFIG_DEV_BLK_INITRD, it became clear that this was
>>>>>> because we define __early_init_dt_declare_initrd() differently and we do
>>>>>> that in arch/arm64/include/asm/memory.h which gets included by a fair
>>>>>> amount of other header files, and translation units as well.
>>>>>
>>>>> I scratch my head sometimes as to why some config options rebuild so
>>>>> much stuff. One down, ? to go. :)
>>>>>
>>>>>> Changing the value of CONFIG_DEV_BLK_INITRD is a common thing with build
>>>>>> systems that generate two kernels: one with the initramfs and one
>>>>>> without. buildroot is one of these build systems, OpenWrt is also
>>>>>> another one that does this.
>>>>>>
>>>>>> This patch series proposes adding an empty initrd.h to satisfy the need
>>>>>> for drivers/of/fdt.c to unconditionally include that file, and moves the
>>>>>> custom __early_init_dt_declare_initrd() definition away from
>>>>>> asm/memory.h
>>>>>>
>>>>>> This cuts the number of objects rebuilds from 1920 down to 26, so a
>>>>>> factor 73 approximately.
>>>>>>
>>>>>> Apologies for the long CC list, please let me know how you would go
>>>>>> about merging that and if another approach would be preferable, e.g:
>>>>>> introducing a CONFIG_ARCH_INITRD_BELOW_START_OK Kconfig option or
>>>>>> something like that.
>>>>>
>>>>> There may be a better way as of 4.20 because bootmem is now gone and
>>>>> only memblock is used. This should unify what each arch needs to do
>>>>> with initrd early. We need the physical address early for memblock
>>>>> reserving. Then later on we need the virtual address to access the
>>>>> initrd. Perhaps we should just change initrd_start and initrd_end to
>>>>> physical addresses (or add 2 new variables would be less invasive and
>>>>> allow for different translation than __va()). The sanity checks and
>>>>> memblock reserve could also perhaps be moved to a common location.
>>>>>
>>>>> Alternatively, given arm64 is the only oddball, I'd be fine with an
>>>>> "if (IS_ENABLED(CONFIG_ARM64))" condition in the default
>>>>> __early_init_dt_declare_initrd as long as we have a path to removing
>>>>> it like the above option.
>>>>
>>>> I think arm64 does not have to redefine __early_init_dt_declare_initrd().
>>>> Something like this might be just all we need (completely untested,
>>>> probably it won't even compile):
>>>>
>>>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>>>> index 9d9582c..e9ca238 100644
>>>> --- a/arch/arm64/mm/init.c
>>>> +++ b/arch/arm64/mm/init.c
>>>> @@ -62,6 +62,9 @@ s64 memstart_addr __ro_after_init = -1;
>>>>  phys_addr_t arm64_dma_phys_limit __ro_after_init;
>>>>
>>>>  #ifdef CONFIG_BLK_DEV_INITRD
>>>> +
>>>> +static phys_addr_t initrd_start_phys, initrd_end_phys;
>>>> +
>>>>  static int __init early_initrd(char *p)
>>>>  {
>>>>         unsigned long start, size;
>>>> @@ -71,8 +74,8 @@ static int __init early_initrd(char *p)
>>>>         if (*endp == ',') {
>>>>                 size = memparse(endp + 1, NULL);
>>>>
>>>> -               initrd_start = start;
>>>> -               initrd_end = start + size;
>>>> +               initrd_start_phys = start;
>>>> +               initrd_end_phys = end;
>>>>         }
>>>>         return 0;
>>>>  }
>>>> @@ -407,14 +410,27 @@ void __init arm64_memblock_init(void)
>>>>                 memblock_add(__pa_symbol(_text), (u64)(_end - _text));
>>>>         }
>>>>
>>>> -       if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && initrd_start) {
>>>> +       if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) &&
>>>> +           (initrd_start || initrd_start_phys)) {
>>>> +               /*
>>>> +                * FIXME: ensure proper precendence between
>>>> +                * early_initrd and DT when both are present
>>>
>>> Command line takes precedence, so just reverse the order.
>>>
>>>> +                */
>>>> +               if (initrd_start) {
>>>> +                       initrd_start_phys = __phys_to_virt(initrd_start);
>>>> +                       initrd_end_phys = __phys_to_virt(initrd_end);
> 
> BTW, I think you meant virt_to_phys() here?
> 
>>>
>>> AIUI, the original issue was doing the P2V translation was happening
>>> too early and the VA could be wrong if the linear range is adjusted.
>>> So I don't think this would work.
>>
>> Probably things have changed since then, but in the current code there is
>>
>>                 initrd_start = __phys_to_virt(initrd_start);
>>
>> and in between only the code related to CONFIG_RANDOMIZE_BASE, so I believe
>> it's safe to use __phys_to_virt() here as well.
> 
> Here is fine yes, but I believe it was the the phys to virt in the DT
> code before adjusting the linear range that was the problem.

FWIW, I am extracting the ARM implementation that parses the initrd
early command line parameter and the "setup" code doing the page
boundary alignment and memblock checking into a helper into lib/ that
other architectures can re-use. So far, this removes the need for
unicore32, arc and arm to duplicate essentially the same logic.
-- 
Florian



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