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From: Dave Hansen <dave.hansen@linux.intel.com>
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Date: Tue, 27 Mar 2018 09:32:27 -0700
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To: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>, Andrea Arcangeli <aarcange@redhat.com>, Andrew Lutomirski <luto@kernel.org>, Kees Cook <keescook@google.com>, Hugh Dickins <hughd@google.com>, =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>, the arch/x86 maintainers <x86@kernel.org>, namit@vmware.com

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.