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Subject: Re: [PATCH v9 1/8] mm: Add per-cpu logic to page shuffling
From:   Alexander Duyck <alexander.h.duyck@linux.intel.com>
To:     David Hildenbrand <david@redhat.com>,
        Alexander Duyck <alexander.duyck@gmail.com>,
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Cc:     yang.zhang.wz@gmail.com, pagupta@redhat.com,
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        ying.huang@intel.com, pbonzini@redhat.com,
        dan.j.williams@intel.com, fengguang.wu@intel.com,
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Date:   Tue, 10 Sep 2019 15:11:50 -0700
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On Mon, 2019-09-09 at 10:14 +0200, David Hildenbrand wrote:
> On 07.09.19 19:25, Alexander Duyck wrote:
> > From: Alexander Duyck <alexander.h.duyck@linux.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.
> 
> So, usually we perform such changes if there is real evidence. Do you
> have any such performance numbers to back your claims?

I don't have any numbers. From what I can tell the impact is small enough
that this doesn't really have much impact.

With that being the case I can probably just drop this patch. I will
instead just use "rand & 1" in the 2nd patch to generate the return value
which was what was previously done in add_to_free_area_random.