linux-kernel - Re: [RFC] x86_64: A real proposal for iret-less return to kernel

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Message-ID: <CA+55aFzx82y5xDa3-6aLm6fCvaf23FH1E14PvmXXUFngwpkdgw@mail.gmail.com>
Date:	Thu, 22 May 2014 07:33:32 +0900
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [RFC] x86_64: A real proposal for iret-less return to kernel

On Thu, May 22, 2014 at 7:25 AM, Andi Kleen <andi@...stfloor.org> wrote:
>
> I suspect the only case that's really interesting here is interrupting
> idle. Maybe it would be possible to do some fast path in this case only.

Hardware-interrupts during kernel are actually fairly common under
network-intensive loads, even outside of idle (but idle is admittedly
likely *the* most common one). Many network loads are fairly
kernel-intensive.

Also, from a kernel perspective, idle isn't really any different from
most other kernel code. Using "ret" to return to the idle handler
would be *more* of a special case than using "ret" to return to just
generic kernel context.

So I disagree vehemently. Do *not* special-case idle. It makes the
code more complex and less generic.

                Linus
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