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

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Message-ID: <alpine.DEB.2.21.1803302230560.1479@nanos.tec.linutronix.de>
Date:   Fri, 30 Mar 2018 22:32:44 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
cc:     Ingo Molnar <mingo@...nel.org>,
        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 Fri, 30 Mar 2018, Dave Hansen wrote:

> On 03/30/2018 05:17 AM, Ingo Molnar wrote:
> > BTW., the expectation on !PCID Intel hardware would be for global pages to help 
> > even more than the 0.6% and 1.7% you measured on PCID hardware: PCID already 
> > _reduces_ the cost of TLB flushes - so if there's not even PCID then global pages 
> > should help even more.
> > 
> > In theory at least. Would still be nice to measure it.
> 
> I did the lseek test on a modern, non-PCID system:
> 
> No Global pages (baseline): 6077741 lseeks/sec
> 94 Global pages (this set): 8433111 lseeks/sec
> 			   +2355370 lseeks/sec (+38.8%)

That's all kernel text, right? What's the result for the case where global
is only set for all user/kernel shared pages?

Thanks,

	tglx