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Date:   Thu, 25 Feb 2021 10:55:00 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Nadav Amit <nadav.amit@gmail.com>
Cc:     Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>,
        Hugh Dickins <hughd@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Sean Christopherson <seanjc@google.com>,
        Andrew Morton <akpm@linux-foundation.org>, x86@kernel.org
Subject: Re: [RFC 0/6] x86: prefetch_page() vDSO call
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References: <20210225072910.2811795-1-namit@vmware.com>
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 <64538CCF-AD11-43C2-9632-E054301F9E6D@gmail.com>
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On Thu, Feb 25, 2021 at 01:32:56AM -0800, Nadav Amit wrote:
> > On Feb 25, 2021, at 12:52 AM, Nadav Amit <nadav.amit@gmail.com> wrote:

> > Can you give me a reference to the =E2=80=9Cremoving explicit prefetch =
=66rom some
> > parts of the kernel=E2=80=9D?

75d65a425c01 ("hlist: remove software prefetching in hlist iterators")
e66eed651fd1 ("list: remove prefetching from regular list iterators")

> Oh. I get it - you mean we remove we remove the use of explicit memory
> prefetch from the kernel code. Well, I don=E2=80=99t think it is really r=
elated,
> but yes, performance numbers are needed.

Right, so my main worry was that use of the prefetch instruction
actually hurt performance once the hardware prefetchers got smart
enough, this being a very similar construct (just on a different level
of the stack) should be careful not to suffer the same fate.