linux-kernel - Re: [tip:x86/asm] sched/x86_64: Don't save flags on context switch

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Message-ID: <20141103215837.GB8711@redhat.com>
Date:	Mon, 3 Nov 2014 22:58:37 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Jan Beulich <jbeulich@...e.com>, Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Sebastian Lackner <sebastian@...-team.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Chuck Ebbert <cebbert.lkml@...il.com>,
	Anish Bhatt <anish@...lsio.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/asm] sched/x86_64: Don't save flags on context switch

On 11/03, Oleg Nesterov wrote:
>
> On 11/03, Andy Lutomirski wrote:
> >
> > And do we ever have TF set during a context switch?  I hope not.
>
> I too hope.
>
> > Also, what's with 'jmp exit_intr' at the end of retint_kernel?  Why
> > isn't that 'jmp retint_kernel'?
>
> Even better, why not "jmp retint_restore_args" ?
>
> preempt_schedule_irq() checks need_resched() and returns with irqs
> disabled, not need to to recheck test_preempt_need_resched() ?

Btw, why retint_kernel() checks "interrupts on" ? It seems to me that
that "interrupts off" is not possible, no? And this will be more clear
when we remove the "exit_intr" label.

Oleg.

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