linux-kernel - Re: [PATCH 4/7] x86/intel_rdt: Implement scheduling support for Intel RDT

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Date:	Thu, 7 May 2015 16:15:41 -0700 (PDT)
From:	Vikas Shivappa <vikas.shivappa@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Vikas Shivappa <vikas.shivappa@...el.com>,
	Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
	tglx@...utronix.de, mingo@...nel.org, tj@...nel.org,
	matt.fleming@...el.com, will.auld@...el.com,
	peter.zijlstra@...el.com, h.peter.anvin@...el.com,
	kanaka.d.juvva@...el.com
Subject: Re: [PATCH 4/7] x86/intel_rdt: Implement scheduling support for
 Intel RDT



On Wed, 6 May 2015, Peter Zijlstra wrote:

> On Mon, May 04, 2015 at 11:39:21AM -0700, Vikas Shivappa wrote:
>
>>>> --- a/arch/x86/include/asm/switch_to.h
>>>> +++ b/arch/x86/include/asm/switch_to.h
>>>> @@ -8,6 +8,9 @@ struct tss_struct;
>>>> void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
>>>> 		      struct tss_struct *tss);
>>>>
>>>> +#include <asm/intel_rdt.h>
>>>> +#define post_arch_switch(current)	rdt_sched_in(current)
>>>> +
>>>> #ifdef CONFIG_X86_32
>>>>
>>>> #ifdef CONFIG_CC_STACKPROTECTOR
>>>
>>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>>>> index f9123a8..cacb490 100644
>>>> --- a/kernel/sched/core.c
>>>> +++ b/kernel/sched/core.c
>>>> @@ -2241,6 +2241,7 @@ static struct rq *finish_task_switch(struct task_struct *prev)
>>>> 	prev_state = prev->state;
>>>> 	vtime_task_switch(prev);
>>>> 	finish_arch_switch(prev);
>>>> +	post_arch_switch(current);
>>>> 	perf_event_task_sched_in(prev, current);
>>>> 	finish_lock_switch(rq, prev);
>>>> 	finish_arch_post_lock_switch();
>>>
>>> Not a word in the Changelog on this hook; that's double fail.
>>
>> will add the changelog. we want the current task which no other existing
>> hook provides.
>
> No.
>
> 1) two arch hooks right after one another is FAIL
> 1a) just 'fix' the existing hook
> 2) current is cheap and easily obtainable without passing it as
>    an argument

will fix to just use an existing hook in finish_task_switch and 
current(get_current) since the stack would already be changed ..

Thanks,
Vikas

> 3) why do you need the hook in the first place?
> 3a) why can't you put this in __switch_to()? This is very much x86 only
>     code.
>
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