From: Dave Hansen <dave.hansen@linux.intel.com>
To: Ingo Molnar <mingo@kernel.org>, 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>,
"Jürgen Groß" <jgross@suse.com>,
"the arch/x86 maintainers" <x86@kernel.org>,
namit@vmware.com
Subject: Re: [PATCH 00/11] Use global pages with PTI
Date: Tue, 27 Mar 2018 13:19:40 -0700 [thread overview]
Message-ID: <a3837d26-031f-6bce-cb1e-f34e5c0cfd2f@linux.intel.com> (raw)
In-Reply-To: <20180327200719.lvdomez6hszpmo4s@gmail.com>
On 03/27/2018 01:07 PM, Ingo Molnar wrote:
> - To see at minimum stddev numbers, to make sure we are not looking at some weird
> statistical artifact. (I also outlined a more robust measurement method.)
>
> - If the numbers are right, a CPU engineer should have a look if possible,
> because frankly this effect is not expected and is not intuitive. Where global
> pages can be used safely they are almost always an unconditional win.
> Maybe we are missing some limitation or some interaction with PCID.
>
> Since we'll be using PCID even on Meltdown-fixed hardware, maybe the same negative
> performance effect already exists on non-PTI kernels as well, we just never
> noticed?
Yep, totally agree. I'll do the more robust collection and also explore
on "real" !PCID hardware. I also know the right CPU folks to go ask
about this, I just want to do the second round of robust data collection
before I bug them.
next prev parent reply other threads:[~2018-03-27 20:19 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-23 17:44 [PATCH 00/11] Use global pages with PTI Dave Hansen
2018-03-23 17:44 ` [PATCH 01/11] x86/mm: factor out pageattr _PAGE_GLOBAL setting Dave Hansen
2018-03-23 17:44 ` [PATCH 02/11] x86/mm: undo double _PAGE_PSE clearing Dave Hansen
2018-03-23 17:44 ` [PATCH 03/11] x86/mm: introduce "default" kernel PTE mask Dave Hansen
2018-03-23 17:44 ` [PATCH 04/11] x86/espfix: document use of _PAGE_GLOBAL Dave Hansen
2018-03-23 17:44 ` [PATCH 05/11] x86/mm: do not auto-massage page protections Dave Hansen
2018-03-23 19:15 ` Nadav Amit
2018-03-23 19:26 ` Dave Hansen
2018-03-23 19:26 ` Dave Hansen
2018-03-23 19:34 ` Nadav Amit
2018-03-23 19:38 ` Dave Hansen
2018-03-24 15:10 ` kbuild test robot
2018-03-24 15:10 ` kbuild test robot
2018-03-24 15:21 ` kbuild test robot
2018-03-24 15:21 ` kbuild test robot
2018-03-23 17:44 ` [PATCH 06/11] x86/mm: remove extra filtering in pageattr code Dave Hansen
2018-03-23 17:44 ` [PATCH 07/11] x86/mm: comment _PAGE_GLOBAL mystery Dave Hansen
2018-03-23 17:44 ` [PATCH 08/11] x86/mm: do not forbid _PAGE_RW before init for __ro_after_init Dave Hansen
2018-03-23 17:45 ` [PATCH 09/11] x86/pti: enable global pages for shared areas Dave Hansen
2018-03-23 19:12 ` Nadav Amit
2018-03-23 19:36 ` Dave Hansen
2018-03-23 17:45 ` [PATCH 10/11] x86/pti: clear _PAGE_GLOBAL for kernel image Dave Hansen
2018-03-23 17:45 ` [PATCH 11/11] x86/pti: leave kernel text global for !PCID Dave Hansen
2018-03-23 18:26 ` [PATCH 00/11] Use global pages with PTI Linus Torvalds
2018-03-24 0:40 ` Dave Hansen
2018-03-24 0:46 ` Linus Torvalds
2018-03-24 0:54 ` Linus Torvalds
2018-03-24 11:05 ` Ingo Molnar
2018-03-27 13:36 ` Thomas Gleixner
2018-03-27 16:32 ` Dave Hansen
2018-03-27 17:51 ` Thomas Gleixner
2018-03-27 20:07 ` Ingo Molnar
2018-03-27 20:19 ` Dave Hansen [this message]
2018-03-29 0:17 ` Dave Hansen
2018-03-30 12:09 ` Ingo Molnar
2018-03-30 12:17 ` Ingo Molnar
2018-03-30 20:26 ` Dave Hansen
2018-03-30 20:32 ` Thomas Gleixner
2018-03-30 21:40 ` Dave Hansen
2018-03-31 5:39 ` Ingo Molnar
2018-03-31 18:19 ` Dave Hansen
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