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

[Kostiantyn Iarmak <kiarmak@xxxxxxxxx>]

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@xxxxxxxxxx>
> > 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@xxxxxxx>
> > Cc: mark.rutland@xxxxxxx, bhe@xxxxxxxxxx, kexec@xxxxxxxxxxxxxxxxxxx,
> > horms@xxxxxxxxxxxx, dyoung@xxxxxxxxxx,
> > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> >
> >
> > 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@xxxxxxxxxxxxxxxxxxx
> > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

--
Best Regards,

  Kostiantyn (Kostia) Iarmak.


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