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

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Date:	Mon, 3 Nov 2014 14:37:07 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Oleg Nesterov <oleg@...hat.com>
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 Mon, Nov 3, 2014 at 1:58 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> 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() ?

Seems reasonable to me.  Want to write the patch?

>
> 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.

We might get there from #MC or from any of a number of synchronous
errors (#GP from xyz_safe, #PF from some atomic uaccess thing or a
vmap fault, etc), and all of those have interrupts off.

--Andy

>
> Oleg.
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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