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Date: Mon, 6 Apr 2015 15:42:53 +1000 (EST)
From: Bruce Evans <brde@optusnet.com.au>
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To: Eitan Adler <eadler@freebsd.org>
Subject: Re: svn commit: r281103 - head/sys/amd64/amd64
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On Mon, 6 Apr 2015, Eitan Adler wrote:

> + a few people interested in the diff
>
> On 5 April 2015 at 02:55, Bruce Evans <brde@optusnet.com.au> wrote:
>> On Sun, 5 Apr 2015, Eitan Adler wrote:
>
> I did not confirm the performance impact, but the submitter and others
> indicated they saw a difference.
>
> Do you have specific data that shows that there was an improvement?

Only micro-benchmark output that indicates little difference.  This
is probably very MD (depending on write combining hardware), so you
might only see a difference on some systems.

I also have micro-benchmark output for network packets/second that
shows 10% differences for the change of adding 1 byte of padding
in code that is never executed.  This seems to be due to different
cache misses.  To eliminate differences from this (except ones
caused by actually running different code), create a reference
version by padding the functions or data to be changed so that
the change doesn't affect the address of anything except the
internals of the changed parts.

I might try a makeworld run to see if changing the non-temporal
accesses in pagecopy and pagezero to cached.

Bruce