linux-kernel - Re: [PATCH v8 1/7] mm: Add per-cpu logic to page shuffling

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Date:   Fri, 6 Sep 2019 10:33:42 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     nitesh@...hat.com, KVM list <kvm@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        virtio-dev@...ts.oasis-open.org,
        Oscar Salvador <osalvador@...e.de>, yang.zhang.wz@...il.com,
        Pankaj Gupta <pagupta@...hat.com>,
        Rik van Riel <riel@...riel.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        lcapitulino@...hat.com, "Wang, Wei W" <wei.w.wang@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Subject: Re: [PATCH v8 1/7] mm: Add per-cpu logic to page shuffling

On Fri, Sep 6, 2019 at 7:53 AM Alexander Duyck
<alexander.duyck@...il.com> wrote:
>
> From: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
>
> Change the logic used to generate randomness in the suffle path so that we
> can avoid cache line bouncing. The previous logic was sharing the offset
> and entropy word between all CPUs. As such this can result in cache line
> bouncing and will ultimately hurt performance when enabled.
>
> To resolve this I have moved to a per-cpu logic for maintaining a unsigned
> long containing some amount of bits, and an offset value for which bit we
> can use for entropy with each call.
>

Reviewed-by: Dan Williams <dan.j.williams@...el.com>