linux-kernel - Re: [RFC 09/13] x86/mm: Disable interrupts when flushing the TLB using CR3

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Message-ID: <CALCETrVTO9NoxW-6zEAhHCa2ttQTKA0B+_0OCY-Qe10SwuTFag@mail.gmail.com>
Date:	Wed, 13 Jan 2016 15:51:35 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Dave Hansen <dave.hansen@...ux.intel.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, X86 ML <x86@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Brian Gerst <brgerst@...il.com>
Subject: Re: [RFC 09/13] x86/mm: Disable interrupts when flushing the TLB
 using CR3

On Wed, Jan 13, 2016 at 3:43 PM, Dave Hansen
<dave.hansen@...ux.intel.com> wrote:
> On 01/13/2016 03:35 PM, Andy Lutomirski wrote:
>> Can anyone here ask a hardware or microcode person what's going on
>> with CR3 writes possibly being faster than INVPCID?  Is there some
>> trick to it?
>
> I just went and measured it myself this morning.  "INVPCID Type 3" (all
> contexts no global) on a Skylake system was 15% slower than a CR3 write.
>
> Is that in the same ballpark from what you've observed?
>
>

It's similar, except that I was comparing "INVPCID Type 1" (single
context no globals) to a CR3 write.

Type 2, at least, is dramatically faster than the pair of CR4 writes
it replaces.

--Andy