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From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>, X86 ML <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Juergen Gross <jgross@suse.com>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>,
	Kees Cook <keescook@chromium.org>
Subject: Re: [RFC 00/17] Pile o' entry stack changes
Date: Thu, 7 Sep 2017 09:04:46 +0200	[thread overview]
Message-ID: <20170907070446.uu2tzul45r76kj3o@gmail.com> (raw)
In-Reply-To: <CALCETrXztQ+z+pBDz5Ru6y3e_1uf1xaxkVmOuboDE1uX9vL=hw@mail.gmail.com>


* Andy Lutomirski <luto@kernel.org> wrote:

> On Wed, Sep 6, 2017 at 3:16 PM, Andi Kleen <andi@firstfloor.org> wrote:
> > Andy Lutomirski <luto@kernel.org> writes:
> >>
> >>  - Lots of people (Linus included) have asked to convert the entry
> >>    code to pop registers on exit instead of movqing them off the
> >>    stack.  This makes a bunch of progress in that direction.
> >
> > You should benchmark it on Atoms. Likely it's a regression there
> > because they don't have the special PUSH/POP acceleration.
> 
> I'm not entirely sure this is a worthwhile reason.  Atom will lose a
> few cycles due to POP throughput, but there's a lot less decode
> bandwidth needed and we save a cache line or two.

I think we can also safely assume that Atom will eventually either join the
21st century or die out - mild Atom micro-costs are not a good reason to
complicate the entry code...

Thanks,

	Ingo

      reply	other threads:[~2017-09-07  7:04 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-06 21:36 [RFC 00/17] Pile o' entry stack changes Andy Lutomirski
2017-09-06 21:36 ` [RFC 01/17] x86/asm/64: Remove the restore_c_regs_and_iret label Andy Lutomirski
2017-09-07  9:40   ` Borislav Petkov
2017-09-07  9:46     ` Ingo Molnar
2017-09-07  9:49       ` Ingo Molnar
2017-09-07  9:57         ` Borislav Petkov
2017-09-07 10:29           ` Ingo Molnar
2017-09-06 21:36 ` [RFC 02/17] x86/asm/64: Split the iret-to-user and iret-to-kernel paths Andy Lutomirski
2017-09-06 21:36 ` [RFC 03/17] x86/asm/64: Move SWAPGS into the common iret-to-usermode path Andy Lutomirski
2017-09-06 21:36 ` [RFC 04/17] x86/asm/64: Simplify reg restore code in the standard IRET paths Andy Lutomirski
2017-09-12 20:05   ` Josh Poimboeuf
2017-09-06 21:36 ` [RFC 05/17] x86/asm/64: Shrink paranoid_exit_restore and make labels local Andy Lutomirski
2017-09-06 21:36 ` [RFC 06/17] x86/asm/64: Use pop instead of movq in syscall_return_via_sysret Andy Lutomirski
2017-09-06 21:36 ` [RFC 07/17] x86/asm/64: Merge the fast and slow SYSRET paths Andy Lutomirski
2017-09-06 21:36 ` [RFC 08/17] x86/asm/64: De-Xen-ify our NMI code Andy Lutomirski
2017-09-07  9:34   ` Juergen Gross
2017-09-07 18:38     ` Andy Lutomirski
2017-09-08  4:26       ` Juergen Gross
2017-09-06 21:36 ` [RFC 09/17] x86/asm/32: Pull MSR_IA32_SYSENTER_CS update code out of native_load_sp0() Andy Lutomirski
2017-09-12 20:06   ` Josh Poimboeuf
2017-09-06 21:36 ` [RFC 10/17] x86/asm/64: Pass sp0 directly to load_sp0() Andy Lutomirski
2017-09-06 21:36 ` [RFC 11/17] x86/asm: Add task_top_of_stack() to find the top of a task's stack Andy Lutomirski
2017-09-06 21:36 ` [RFC 12/17] x86/xen/64: Clean up SP code in cpu_initialize_context() Andy Lutomirski
2017-09-12 20:09   ` Josh Poimboeuf
2017-09-06 21:36 ` [RFC 13/17] x86/boot/64: Stop initializing TSS.sp0 at boot Andy Lutomirski
2017-09-06 21:36 ` [RFC 14/17] x86/asm/64: Remove all remaining direct thread_struct::sp0 reads Andy Lutomirski
2017-09-06 21:37 ` [RFC 15/17] x86/boot/32: Fix cpu_current_top_of_stack initialization at boot Andy Lutomirski
2017-09-06 21:37 ` [RFC 16/17] x86/asm/64: Remove thread_struct::sp0 Andy Lutomirski
2017-09-06 21:37 ` [RFC 17/17] x86/traps: Use a new on_thread_stack() helper to clean up an assertion Andy Lutomirski
2017-09-12 20:11   ` Josh Poimboeuf
2017-09-12 20:25     ` Andrew Cooper
2017-09-06 22:16 ` [RFC 00/17] Pile o' entry stack changes Andi Kleen
2017-09-07  0:01   ` Andy Lutomirski
2017-09-07  7:04     ` Ingo Molnar [this message]

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