linux-kernel - Re: [PATCH 00/11] Use global pages with PTI

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Message-ID: <c0e7ca0b-dcb5-66e2-9df6-f53e4eb22781@linux.intel.com>
Date:   Tue, 27 Mar 2018 09:32:27 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jürgen Groß <jgross@...e.com>,
        the arch/x86 maintainers <x86@...nel.org>, namit@...are.com
Subject: Re: [PATCH 00/11] Use global pages with PTI

On 03/27/2018 06:36 AM, Thomas Gleixner wrote:
>>                         User Time       Kernel Time     Clock Elapsed
>> Baseline ( 0 GLB PTEs)  803.79          67.77           237.30
>> w/series (28 GLB PTEs)  807.70 (+0.7%)  68.07 (+0.7%)   238.07 (+0.3%)
>>
>> Without PCIDs, it behaves the way I would expect.
> What's the performance benefit on !PCID systems? And I mean systems which
> actually do not have PCID, not a PCID system with 'nopcid' on the command
> line.

Do you have something in mind for this?  Basically *all* of the servers
that I have access to have PCID because they are newer than ~7 years old.

That leaves *some* Ivybridge and earlier desktops, Atoms and AMD
systems.  Atoms are going to be the easiest thing to get my hands on,
but I tend to shy away from them for performance work.