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Date: Fri, 30 Mar 2018 14:09:20 +0200
From: Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH 00/11] Use global pages with PTI
Message-ID: <20180330120920.btobga44wqytlkoe@gmail.com>
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To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, 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>, =?iso-8859-1?Q?J=FCrgen_Gro=DF?= <jgross@suse.com>, the arch/x86 maintainers <x86@kernel.org>, namit@vmware.com


* Dave Hansen <dave.hansen@linux.intel.com> wrote:

> On 03/27/2018 01:07 PM, Ingo Molnar wrote:
> > * Thomas Gleixner <tglx@linutronix.de> wrote:
> >>> 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.
> >> What I have in mind is that I wonder whether the whole circus is worth it
> >> when there is no performance advantage on PCID systems.
> 
> I was waiting on trying to find a relatively recent Atom system (they
> actually come in reasonably sized servers [1]), but I'm hitting a snag
> there, so I figured I'd just share a kernel compile using Ingo's
> perf-based methodology on a Skylake desktop system with PCIDs.
>
> Here's the kernel compile:
> 
> No Global pages (baseline): 186.951 seconds time elapsed  ( +-  0.35% )
> 28 Global pages (this set): 185.756 seconds time elapsed  ( +-  0.09% )
>                              -1.195 seconds (-0.64%)
> 
> Lower is better here, obviously.
> 
> I also re-checked everything using will-it-scale's llseek1 test[2] which
> is basically a microbenchmark of a halfway reasonable syscall.  Higher
> here is better.
> 
> No Global pages (baseline): 15783951 lseeks/sec
> 28 Global pages (this set): 16054688 lseeks/sec
> 			     +270737 lseeks/sec (+1.71%)
> 
> So, both the kernel compile and the microbenchmark got measurably faster.

Ok, cool, this is much better!

Mind re-sending the patch-set against latest -tip so it can be merged?

At this point !PCID Intel hardware is not a primary concern, if something bad 
happens on them with global pages we can quirk global pages off on them in some 
way, or so.

Thanks,

	Ingo