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From: Matthew Wilcox <willy@infradead.org>
To: Andi Kleen <ak@linux.intel.com>
Cc: Michal Hocko <mhocko@kernel.org>,
	"Kirill A. Shutemov" <kirill@shutemov.name>,
	Cannon Matthews <cannonmatthews@google.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Rientjes <rientjes@google.com>,
	Greg Thelen <gthelen@google.com>, Salman Qazi <sqazi@google.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH] mm: clear 1G pages with streaming stores on x86
Date: Mon, 9 Mar 2020 11:37:04 -0700	[thread overview]
Message-ID: <20200309183704.GA1573@bombadil.infradead.org> (raw)
In-Reply-To: <20200309153831.GK1454533@tassilo.jf.intel.com>

On Mon, Mar 09, 2020 at 08:38:31AM -0700, Andi Kleen wrote:
> > Gigantic huge pages are a bit different. They are much less dynamic from
> > the usage POV in my experience. Micro-optimizations for the first access
> > tends to not matter at all as it is usually pre-allocation scenario. On
> > the other hand, speeding up the initialization sounds like a good thing
> > in general. It will be a single time benefit but if the additional code
> > is not hard to maintain then I would be inclined to take it even with
> > "artificial" numbers state above. There really shouldn't be other downsides
> > except for the code maintenance, right?
> 
> There's a cautious tale of the old crappy RAID5 XOR assembler functions which
> were optimized a long time ago for the Pentium1, and stayed around,
> even though the compiler could actually do a better job.
> 
> String instructions are constantly improving in performance (Broadwell is
> very old at this point) Most likely over time (and maybe even today
> on newer CPUs) you would need much more sophisticated unrolled MOVNTI variants
> (or maybe even AVX-*) to be competitive.

Presumably you have access to current and maybe even some unreleased
CPUs ... I mean, he's posted the patches, so you can test this hypothesis.

  reply	other threads:[~2020-03-09 18:37 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-07  1:03 Cannon Matthews
2020-03-07 22:06 ` Andrew Morton
2020-03-09  0:08 ` Kirill A. Shutemov
2020-03-09  9:06   ` Michal Hocko
2020-03-09  9:35     ` Kirill A. Shutemov
2020-03-09 11:36     ` Kirill A. Shutemov
2020-03-09 12:26       ` Michal Hocko
2020-03-09 18:01         ` Mike Kravetz
2020-03-09 15:38     ` Andi Kleen
2020-03-09 18:37       ` Matthew Wilcox [this message]
2020-03-11  0:21         ` Cannon Matthews
2020-03-11  0:54           ` Kirill A. Shutemov
2020-03-11  3:35             ` Arvind Sankar
2020-03-11  8:16               ` Kirill A. Shutemov
2020-03-11 18:32                 ` Arvind Sankar
2020-03-11 20:32                   ` Arvind Sankar
2020-03-12  0:52                     ` Kirill A. Shutemov
2020-03-31  0:40                   ` Elliott, Robert (Servers)
2020-03-16 10:18             ` Michal Hocko
2020-03-16 12:19               ` Kirill A. Shutemov
2020-03-26 19:46                 ` Matthew Wilcox
2020-03-11 15:07       ` David Laight
2020-03-09 15:33   ` Andi Kleen

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