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Date: Wed, 20 Dec 2023 15:00:21 +0100
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Subject: Re: [PATCH v4 02/16] mm: Batch-copy PTE ranges during fork()
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To: Ryan Roberts <ryan.roberts@arm.com>,
 Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>,
 Ard Biesheuvel <ardb@kernel.org>, Marc Zyngier <maz@kernel.org>,
 Oliver Upton <oliver.upton@linux.dev>, James Morse <james.morse@arm.com>,
 Suzuki K Poulose <suzuki.poulose@arm.com>, Zenghui Yu
 <yuzenghui@huawei.com>, Andrey Ryabinin <ryabinin.a.a@gmail.com>,
 Alexander Potapenko <glider@google.com>,
 Andrey Konovalov <andreyknvl@gmail.com>, Dmitry Vyukov <dvyukov@google.com>,
 Vincenzo Frascino <vincenzo.frascino@arm.com>,
 Andrew Morton <akpm@linux-foundation.org>,
 Anshuman Khandual <anshuman.khandual@arm.com>,
 Matthew Wilcox <willy@infradead.org>, Yu Zhao <yuzhao@google.com>,
 Mark Rutland <mark.rutland@arm.com>, Kefeng Wang
 <wangkefeng.wang@huawei.com>, John Hubbard <jhubbard@nvidia.com>,
 Zi Yan <ziy@nvidia.com>, Barry Song <21cnbao@gmail.com>,
 Alistair Popple <apopple@nvidia.com>, Yang Shi <shy828301@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
 linux-kernel@vger.kernel.org
References: <20231218105100.172635-1-ryan.roberts@arm.com>
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 <dd227e51-c4b2-420b-a92a-65da85ab4018@arm.com>
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 <9a58b1a2-2c13-4fa0-8ffa-2b3d9655f1b6@arm.com>
 <28968568-f920-47ac-b6fd-87528ffd8f77@redhat.com>
 <10b0b562-c1c0-4a66-9aeb-a6bff5c218f6@arm.com>
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 <ade26f27-03af-4ad7-ad81-38b482f7572c@arm.com>
 <3194b8a5-3f72-4d9e-a267-fbdad32ad864@redhat.com>
 <f2f420cf-678d-466d-ac30-bc8251f16632@arm.com>
 <9f99a3ca-051e-4b1b-81e9-8456d8e422ad@redhat.com>
 <c1913fa2-d313-4f05-a649-da69b6d31d2a@arm.com>
 <c244707c-8c0c-4593-ab45-d8f165dbc5ee@redhat.com>
 <ba6a5c11-34fb-40ca-b24a-f51a207464f2@arm.com>
From: David Hildenbrand <david@redhat.com>
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[...]

>>>
>>
>> gcc version 13.2.1 20231011 (Red Hat 13.2.1-4) (GCC)
>>
>>  From Fedora 38. So "a bit" newer :P
>>
> 
> I'll retry with newer toolchain.
> 
> FWIW, with the code fix and the original compiler:
> 
> Fork, order-0, Apple M2:
> | kernel                |   mean_rel |   std_rel |
> |:----------------------|-----------:|----------:|
> | mm-unstable           |       0.0% |      0.8% |
> | hugetlb-rmap-cleanups |       1.3% |      2.0% |
> | fork-batching         |       4.3% |      1.0% |
> 
> Fork, order-9, Apple M2:
> | kernel                |   mean_rel |   std_rel |
> |:----------------------|-----------:|----------:|
> | mm-unstable           |       0.0% |      0.8% |
> | hugetlb-rmap-cleanups |       0.9% |      0.9% |
> | fork-batching         |     -37.3% |      1.0% |
> 
> Fork, order-0, Ampere Altra:
> | kernel                |   mean_rel |   std_rel |
> |:----------------------|-----------:|----------:|
> | mm-unstable           |       0.0% |      0.7% |
> | hugetlb-rmap-cleanups |       3.2% |      0.7% |
> | fork-batching         |       5.5% |      1.1% |
> 
> Fork, order-9, Ampere Altra:
> | kernel                |   mean_rel |   std_rel |
> |:----------------------|-----------:|----------:|
> | mm-unstable           |       0.0% |      0.1% |
> | hugetlb-rmap-cleanups |       0.5% |      0.1% |
> | fork-batching         |     -10.4% |      0.1% |
> 

I just gave it another quick benchmark run on that Intel system.

hugetlb-rmap-cleanups -> fork-batching

order-0: 0.014114 -> 0.013848

-1.9%

order-9: 0.014262 -> 0.009410

-34%

Note that I disable SMT and turbo, and pin the test to one CPU, to make 
the results as stable as possible. My kernel config has anything related 
to debugging disabled.

-- 
Cheers,

David / dhildenb