linux-kernel - Re: [PATCH v2 4/6] x86: Rewrite switch

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Message-ID: <20160620154413.awnzmk6wr67vw5ae@treble>
Date:	Mon, 20 Jun 2016 10:44:13 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Brian Gerst <brgerst@...il.com>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 4/6] x86: Rewrite switch_to() code

On Sat, Jun 18, 2016 at 04:56:16PM -0400, Brian Gerst wrote:
> Move the low-level context switch code to an out-of-line asm stub instead of
> using complex inline asm.  This allows constructing a new stack frame for the
> child process to make it seamlessly flow to ret_from_fork without an extra
> test and branch in __switch_to().  It also improves code generation for
> __schedule() by using the C calling convention instead of clobbering all
> registers.
> 
> Signed-off-by: Brian Gerst <brgerst@...il.com>

You can also remove the STACK_FRAME_NON_STANDARD annotation for
__schedule() in kernel/sched/core.c since it no longer produces an
objtool warning.

Otherwise it looks great:

Reviewed-by: Josh Poimboeuf <jpoimboe@...hat.com>

-- 
Josh