linux-kernel - Re: [PATCH 01/22] sched: Provide scheduler_ipi() callback in response to smp_send

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Message-ID: <4D797C88.7080607@am.sony.com>
Date:	Thu, 10 Mar 2011 17:36:08 -0800
From:	Frank Rowand <frank.rowand@...sony.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Chris Mason <chris.mason@...cle.com>,
	"Rowand, Frank" <Frank_Rowand@...yusa.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mike Galbraith <efault@....de>,
	Oleg Nesterov <oleg@...hat.com>, Paul Turner <pjt@...gle.com>,
	Jens Axboe <axboe@...nel.dk>,
	Yong Zhang <yong.zhang0@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Jesper Nilsson <jesper.nilsson@...s.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [PATCH 01/22] sched: Provide scheduler_ipi() callback in response
 to smp_send_reschedule()

On 03/02/11 09:38, Peter Zijlstra wrote:
> For future rework of try_to_wake_up() we'd like to push part of that
> onto the CPU the task is actually going to run on, in order to do so we
> need a generic callback from the existing scheduler IPI.
> 
> This patch introduces such a generic callback: scheduler_ipi() and
> implements it as a NOP.
> 
> BenH notes: PowerPC might use this IPI on offline CPUs under rare
> conditions!!
> 
> Acked-by: Russell King <rmk+kernel@....linux.org.uk>
> Acked-by: Martin Schwidefsky <schwidefsky@...ibm.com>
> Acked-by: Chris Metcalf <cmetcalf@...era.com>
> Acked-by: Jesper Nilsson <jesper.nilsson@...s.com>
> Acked-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Signed-off-by: Ralf Baechle <ralf@...ux-mips.org>
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> LKML-Reference: <new-submission>
> ---
>  arch/alpha/kernel/smp.c             |    3 +--
>  arch/arm/kernel/smp.c               |    5 +----
>  arch/blackfin/mach-common/smp.c     |    3 +++
>  arch/cris/arch-v32/kernel/smp.c     |   13 ++++++++-----
>  arch/ia64/kernel/irq_ia64.c         |    2 ++
>  arch/ia64/xen/irq_xen.c             |   10 +++++++++-
>  arch/m32r/kernel/smp.c              |    4 +---
>  arch/mips/cavium-octeon/smp.c       |    2 ++
>  arch/mips/kernel/smtc.c             |    2 +-
>  arch/mips/mti-malta/malta-int.c     |    2 ++
>  arch/mips/pmc-sierra/yosemite/smp.c |    4 ++++
>  arch/mips/sgi-ip27/ip27-irq.c       |    2 ++
>  arch/mips/sibyte/bcm1480/smp.c      |    7 +++----
>  arch/mips/sibyte/sb1250/smp.c       |    7 +++----
>  arch/mn10300/kernel/smp.c           |    5 +----
>  arch/parisc/kernel/smp.c            |    5 +----
>  arch/powerpc/kernel/smp.c           |    3 ++-
>  arch/s390/kernel/smp.c              |    6 +++---
>  arch/sh/kernel/smp.c                |    2 ++
>  arch/sparc/kernel/smp_32.c          |    2 +-
>  arch/sparc/kernel/smp_64.c          |    1 +
>  arch/tile/kernel/smp.c              |    6 +-----
>  arch/um/kernel/smp.c                |    2 +-
>  arch/x86/kernel/smp.c               |    5 ++---
>  arch/x86/xen/smp.c                  |    5 ++---
>  include/linux/sched.h               |    1 +
>  26 files changed, 60 insertions(+), 49 deletions(-)
> 

< snip >

In this patch the tabs turned into spaces.  (None of the other
patches have this problem.)


> Index: linux-2.6/arch/sparc/kernel/smp_32.c
> ===================================================================
> --- linux-2.6.orig/arch/sparc/kernel/smp_32.c
> +++ linux-2.6/arch/sparc/kernel/smp_32.c
> @@ -125,7 +125,7 @@ struct linux_prom_registers smp_penguin_
> 
>  void smp_send_reschedule(int cpu)
>  {
> -       /* See sparc64 */
> +       scheduler_ipi();
>  }

If I understand correctly, this is calling scheduler_ipi() on the
cpu that should be sending an IPI, not on the cpu receiving the IPI.
If so, smp_send_reschedule() needs to send an IPI, and the scheduler_ipi()
put in the place where the IPI is processed.

-Frank

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