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Date: Tue, 21 May 2024 18:21:39 -0400
From: Eric Chanudet <echanude@redhat.com>
To: Mike Rapoport <rppt@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>, 
	Will Deacon <will@kernel.org>, Baoquan He <bhe@redhat.com>, 
	Andrew Morton <akpm@linux-foundation.org>, Zhen Lei <thunder.leizhen@huawei.com>, 
	Yajun Deng <yajun.deng@linux.dev>, Zhang Jianhua <chris.zjh@huawei.com>, 
	linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Nick Piggin <npiggin@gmail.com>, 
	Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH] arm64: init: override deferred_page_init_max_threads
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References: <20240520231555.395979-5-echanude@redhat.com>
 <ZkzHX-4yYybEJdEQ@kernel.org>
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On Tue, May 21, 2024 at 07:10:07PM +0300, Mike Rapoport wrote:
> (added powerpc folks)
> 
> On Mon, May 20, 2024 at 07:15:59PM -0400, Eric Chanudet wrote:
> > This was the behavior prior to making the function arch-specific with
> > commit ecd096506922 ("mm: make deferred init's max threads
> > arch-specific")
> > 
> > Architectures can override the generic implementation that uses only one
> > CPU. Setting DEFERRED_STRUCT_PAGE_INIT and testing on a few arm64
> > platforms shows faster deferred_init_memmap completions:
> > 
> > |         | x13s        | SA8775p-ride | Ampere R137-P31 | Ampere HR330 |
> > |         | Metal, 32GB | VM, 36GB     | VM, 58GB        | Metal, 128GB |
> > |         | 8cpus       | 8cpus        | 8cpus           | 32cpus       |
> > |---------|-------------|--------------|-----------------|--------------|
> > | threads |  ms     (%) | ms       (%) |  ms         (%) |  ms      (%) |
> > |---------|-------------|--------------|-----------------|--------------|
> > | 1       | 108    (0%) | 72      (0%) | 224        (0%) | 324     (0%) |
> > | cpus    |  24  (-77%) | 36    (-50%) |  40      (-82%) |  56   (-82%) |
> > 
> > Signed-off-by: Eric Chanudet <echanude@redhat.com>
> > ---
> >  arch/arm64/mm/init.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > index 9b5ab6818f7f..71f5188fe63d 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -158,6 +158,13 @@ static void __init zone_sizes_init(void)
> >  	free_area_init(max_zone_pfns);
> >  }
> >  
> > +#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
> > +int __init deferred_page_init_max_threads(const struct cpumask *node_cpumask)
> > +{
> > +	return max_t(int, cpumask_weight(node_cpumask), 1);
> > +}
> > +#endif
> > +
> 
> Maybe we should make this default and let architectures that want a single
> thread override deferred_page_init_max_threads() to return 1?

It would affect more archs than I can try this on. Currently, only x86
(with this change, arm64) return more than one thread.

I'm happy to send a v2 inverting the logic if you find it preferable.

Best,

> >  int pfn_is_map_memory(unsigned long pfn)
> >  {
> >  	phys_addr_t addr = PFN_PHYS(pfn);
> > -- 
> > 2.44.0
> > 
> 
> -- 
> Sincerely yours,
> Mike.
> 

-- 
Eric Chanudet