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Message-ID: <3C3C62BE-6363-41C3-834C-C3124EB3FFAB@joshtriplett.org>
Date: Mon, 04 May 2020 16:38:03 -0700
From: Josh Triplett <josh@...htriplett.org>
To: Alexander Duyck <alexander.duyck@...il.com>,
Daniel Jordan <daniel.m.jordan@...cle.com>
CC: Andrew Morton <akpm@...ux-foundation.org>,
Herbert Xu <herbert@...dor.apana.org.au>,
Steffen Klassert <steffen.klassert@...unet.com>,
Alex Williamson <alex.williamson@...hat.com>,
Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
Dan Williams <dan.j.williams@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
David Hildenbrand <david@...hat.com>,
Jason Gunthorpe <jgg@...pe.ca>,
Jonathan Corbet <corbet@....net>,
Kirill Tkhai <ktkhai@...tuozzo.com>,
Michal Hocko <mhocko@...nel.org>, Pavel Machek <pavel@....cz>,
Pavel Tatashin <pasha.tatashin@...een.com>,
Peter Zijlstra <peterz@...radead.org>,
Randy Dunlap <rdunlap@...radead.org>,
Shile Zhang <shile.zhang@...ux.alibaba.com>,
Tejun Heo <tj@...nel.org>, Zi Yan <ziy@...dia.com>,
linux-crypto@...r.kernel.org, linux-mm <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/7] mm: parallelize deferred_init_memmap()
On May 4, 2020 3:33:58 PM PDT, Alexander Duyck <alexander.duyck@...il.com> wrote:
>On Thu, Apr 30, 2020 at 1:12 PM Daniel Jordan
><daniel.m.jordan@...cle.com> wrote:
>> /*
>> - * Initialize and free pages in MAX_ORDER sized increments so
>> - * that we can avoid introducing any issues with the buddy
>> - * allocator.
>> + * More CPUs always led to greater speedups on tested
>systems, up to
>> + * all the nodes' CPUs. Use all since the system is
>otherwise idle now.
>> */
>
>I would be curious about your data. That isn't what I have seen in the
>past. Typically only up to about 8 or 10 CPUs gives you any benefit,
>beyond that I was usually cache/memory bandwidth bound.
I've found pretty much linear performance up to memory bandwidth, and on the systems I was testing, I didn't saturate memory bandwidth until about the full number of physical cores. From number of cores up to number of threads, the performance stayed about flat; it didn't get any better or worse.
- Josh
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