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

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Message-ID: <3cdc23a2-99eb-6f93-6934-f7757fa30a3e@linux.intel.com>
Date:   Fri, 30 Mar 2018 13:26:14 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        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 03/30/2018 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%)