[PATCH v3 0/2] kexec-tools: arm64: Enable D-cache in purgatory

[Kostiantyn Iarmak]

Unfortunately got delivery failure notification for Pratyush Anand's 
address (Unknown address),

   who can help with merging this patch set?


On 04.04.18 15:45, Kostiantyn Iarmak wrote:
> Hi Pratyush,
>
> From: Pratyush Anand <panand at redhat.com>
>> Date: Fri, Jun 2, 2017 at 5:42 PM
>> Subject: Re: [PATCH v3 0/2] kexec-tools: arm64: Enable D-cache in 
>> purgatory
>> To: James Morse <james.morse at arm.com>
>> Cc: mark.rutland at arm.com, bhe at redhat.com, kexec at lists.infradead.org,
>> horms at verge.net.au, dyoung at redhat.com,
>> linux-arm-kernel at lists.infradead.org
>>
>>
>> Hi James,
>>
>> On Friday 02 June 2017 01:53 PM, James Morse wrote:
>>> Hi Pratyush,
>>>
>>> On 23/05/17 06:02, Pratyush Anand wrote:
>>>> It takes more that 2 minutes to verify SHA in purgatory when 
>>>> vmlinuz image
>>>> is around 13MB and initramfs is around 30MB. It takes more than 20 
>>>> second
>>>> even when we have -O2 optimization enabled. However, if dcache is 
>>>> enabled
>>>> during purgatory execution then, it takes just a second in SHA
>>>> verification.
>>>>
>>>> Therefore, these patches adds support for dcache enabling facility 
>>>> during
>>>> purgatory execution.
>>>
>>> I'm still not convinced we need this. Moving the SHA verification to 
>>> happen
>>> before the dcache+mmu are disabled would also solve the delay problem,
>>
>> Humm..I am not sure, if we can do that.
>>
>> When we leave kernel (and enter into purgatory), icache+dcache+mmu are
>> already disabled. I think, that would be possible when we will be in a
>> position to use in-kernel purgatory.
>>
>>> and we
>>> can print an error message or fail the syscall.
>>>
>>> For kexec we don't expect memory corruption, what are we testing for?
>>> I can see the use for kdump, but the kdump-kernel is unmapped so the 
>>> kernel
>>> can't accidentally write over it.
>>>
>>> (we discussed all this last time, but it fizzled-out. If you and the
>>>   kexec-tools maintainer think its necessary, fine by me!)
>>
>> Yes, there had already been discussion and MAINTAINERs have
>> discouraged none-purgatory implementation.
>>
>>> I have some comments on making this code easier to maintain..
>>>
>> Thanks.
>>
>> I have implemented your review comments and have archived the code in
>>
>> https://github.com/pratyushanand/kexec-tools.git : 
>> purgatory-enable-dcache
>>
>> I will be posting the next version only when someone complains about
>> ARM64 kdump behavior that it is not as fast as x86.
> On our ARM64-based platform we have very long main kernel-secondary 
> kernel switch time.
>
> This patch set fixes the issue (we are using 4.4 kernel and 2.0.13 
> kexec-tools version), we can get ~25x speedup, with this patch 
> secondary kernel boots in ~3 seconds while on 2.0.13-2.0.16 
> kexec-tools without this patch switch takes about 75 seconds.
>
> When do you plan merge this patch?
>
> I can help you with testing on our platform.
>
>> Thanks for all your time on this series. That really helped me to
>> understand the arm64 page table in a better way.
>>
>> ~Pratyush
>>
>>
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel at lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>

-- 
Best Regards,

   Kostiantyn (Kostia) Iarmak.