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

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Date:	Wed, 6 May 2015 09:48:35 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vikas Shivappa <vikas.shivappa@...el.com>
Cc:	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 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
 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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