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Subject: Re: [PATCH 00/11] Use global pages with PTI
References: <20180323174447.55F35636@viggo.jf.intel.com>
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From: Dave Hansen <dave.hansen@linux.intel.com>
Message-ID: <3cdc23a2-99eb-6f93-6934-f7757fa30a3e@linux.intel.com>
Date: Fri, 30 Mar 2018 13:26:14 -0700
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To: Ingo Molnar <mingo@kernel.org>
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>, =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>, the arch/x86 maintainers <x86@kernel.org>, namit@vmware.com

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%)