linux-kernel - Re: [PATCH v4 02/16] mm: Batch-copy PTE ranges during fork()

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Date: Wed, 20 Dec 2023 15:00:21 +0100
From: David Hildenbrand <david@...hat.com>
To: Ryan Roberts <ryan.roberts@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Ard Biesheuvel <ardb@...nel.org>, Marc Zyngier <maz@...nel.org>,
 Oliver Upton <oliver.upton@...ux.dev>, James Morse <james.morse@....com>,
 Suzuki K Poulose <suzuki.poulose@....com>, Zenghui Yu
 <yuzenghui@...wei.com>, Andrey Ryabinin <ryabinin.a.a@...il.com>,
 Alexander Potapenko <glider@...gle.com>,
 Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>,
 Vincenzo Frascino <vincenzo.frascino@....com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Anshuman Khandual <anshuman.khandual@....com>,
 Matthew Wilcox <willy@...radead.org>, Yu Zhao <yuzhao@...gle.com>,
 Mark Rutland <mark.rutland@....com>, Kefeng Wang
 <wangkefeng.wang@...wei.com>, John Hubbard <jhubbard@...dia.com>,
 Zi Yan <ziy@...dia.com>, Barry Song <21cnbao@...il.com>,
 Alistair Popple <apopple@...dia.com>, Yang Shi <shy828301@...il.com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 02/16] mm: Batch-copy PTE ranges during fork()

[...]

>>>
>>
>> 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