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Subject: Re: [PATCH v2] x86: Return to kernel without IRET
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Sat, 03 May 2014 19:14:07 -0700
To: Andy Lutomirski <luto@amacapital.net>
CC: Steven Rostedt <rostedt@goodmis.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        X86 ML <x86@kernel.org>, Gleb Natapov <gleb@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>
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Not for return from NMIs themselves, to be sure

On May 3, 2014 4:51:37 PM PDT, Andy Lutomirski <luto@amacapital.net> wrote:
>On Sat, May 3, 2014 at 3:19 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>> On 05/03/2014 04:24 AM, Steven Rostedt wrote:
>>> On Fri, 02 May 2014 21:03:10 -0700
>>> "H. Peter Anvin" <hpa@zytor.com> wrote:
>>>
>>>>
>>>> I'd really like to see a workload which would genuinely benefit
>before
>>>> adding more complexity.  Now... if we can determine that it doesn't
>harm
>>>> anything and would solve the NMI nesting problem cleaner than the
>>>> current solution, that would justify things, too...
>>>>
>>>
>>> As I stated before. It doesn't solve the NMI nesting problem. It
>only
>>> handles page faults. We would have to implement this for breakpoint
>>> return paths too. Is that a plan as well?
>>>
>>
>> I would assume we would do it for *ALL* the IRETs.  There are only
>three
>> IRETs in the kernel last I checked...
>
>I think we should carefully avoid doing it for returns from NMI, though
>:)
>
>If you want a realistic benchmark that will speed up, packet
>forwarding might be a good place to look.
>
>--Andy

-- 
Sent from my mobile phone.  Please pardon brevity and lack of formatting.