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Re: [PATCH] sched: provide scheduler_ipi() callback in response to smp_s

To: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] sched: provide scheduler_ipi() callback in response to smp_send_reschedule()
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Date: Tue, 18 Jan 2011 07:31:50 +1100
Cc: Richard Henderson <rth@twiddle.net>, Ivan Kokshaysky <ink@jurassic.park.msu.ru>, Matt Turner <mattst88@gmail.com>, Russell King <linux@arm.linux.org.uk>, Mike Frysinger <vapier@gentoo.org>, Mikael Starvik <starvik@axis.com>, Jesper Nilsson <jesper.nilsson@axis.com>, Tony Luck <tony.luck@intel.com>, Fenghua Yu <fenghua.yu@intel.com>, Hirokazu Takata <takata@linux-m32r.org>, Ralf Baechle <ralf@linux-mips.org>, David Howells <dhowells@redhat.com>, Koichi Yasutake <yasutake.koichi@jp.panasonic.com>, Kyle McMartin <kyle@mcmartin.ca>, Helge Deller <deller@gmx.de>, "James E.J. Bottomley" <jejb@parisc-linux.org>, Paul Mackerras <paulus@samba.org>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, linux390@de.ibm.com, Paul Mundt <lethal@linux-sh.org>, "David S. Miller" <davem@davemloft.net>, Chris Metcalf <cmetcalf@tilera.com>, Jeff Dike <jdike@addtoit.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org, Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, uclinux-dist-devel@blackfin.uclinux.org, linux-cris-kernel@axis.com, linux-ia64@vger.kernel.org, linux-m32r@ml.linux-m32r.org, linux-m32r-ja@ml.linux-m32r.org, linux-mips@linux-mips.org, linux-am33-list@redhat.com, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, user-mode-linux-devel@lists.sourceforge.net, user-mode-linux-user@lists.sourceforge.net, xen-devel@lists.xensource.com, virtualization@lists.osdl.org, Linux-Arch <linux-arch@vger.kernel.org>
In-reply-to: <1295262433.30950.53.camel@laptop>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <1295262433.30950.53.camel@laptop>
Sender: linux-mips-bounce@linux-mips.org
On Mon, 2011-01-17 at 12:07 +0100, 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.
> 
> I visited existing smp_send_reschedule() implementations and tried to
> add a call to scheduler_ipi() in their handler part, but esp. for MIPS
> I'm not quite sure I actually got all of them.
> 
> Also, while reading through all this, I noticed the blackfin SMP code
> looks to be broken, it simply discards any IPI when low on memory.

Beware of false positive, I've used "fake" reschedule IPIs in the past
for other things (like kicking a CPU out of sleep state for unrelated
reasons). Nothing that I know that is upstream today but some of that
might come back. I'd like to avoid having to add an atomic to know if
it's a real reschedule, will the scheduler be smart enough to not bother
with false positives ?

Cheers,
Ben.

> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
>  arch/alpha/kernel/smp.c         |    1 +
>  arch/arm/kernel/smp.c           |    1 +
>  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          |    2 +-
>  arch/mips/kernel/smtc.c         |    1 +
>  arch/mips/sibyte/bcm1480/smp.c  |    7 +++----
>  arch/mips/sibyte/sb1250/smp.c   |    7 +++----
>  arch/mn10300/kernel/smp.c       |    2 +-
>  arch/parisc/kernel/smp.c        |    1 +
>  arch/powerpc/kernel/smp.c       |    1 +
>  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          |    1 +
>  arch/um/kernel/smp.c            |    2 +-
>  arch/x86/kernel/smp.c           |    1 +
>  arch/x86/xen/smp.c              |    1 +
>  include/linux/sched.h           |    1 +
>  22 files changed, 46 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/alpha/kernel/smp.c b/arch/alpha/kernel/smp.c
> index 42aa078..c4a570b 100644
> --- a/arch/alpha/kernel/smp.c
> +++ b/arch/alpha/kernel/smp.c
> @@ -587,6 +587,7 @@ handle_ipi(struct pt_regs *regs)
>               case IPI_RESCHEDULE:
>                       /* Reschedule callback.  Everything to be done
>                          is done by the interrupt return path.  */
> +                     scheduler_ipi();
>                       break;
>  
>               case IPI_CALL_FUNC:
> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
> index 9066473..ffde790 100644
> --- a/arch/arm/kernel/smp.c
> +++ b/arch/arm/kernel/smp.c
> @@ -579,6 +579,7 @@ asmlinkage void __exception do_IPI(struct pt_regs *regs)
>                                * nothing more to do - eveything is
>                                * done on the interrupt return path
>                                */
> +                             scheduler_ipi();
>                               break;
>  
>                       case IPI_CALL_FUNC:
> diff --git a/arch/blackfin/mach-common/smp.c b/arch/blackfin/mach-common/smp.c
> index a17107a..e210f8a 100644
> --- a/arch/blackfin/mach-common/smp.c
> +++ b/arch/blackfin/mach-common/smp.c
> @@ -156,6 +156,7 @@ static irqreturn_t ipi_handler(int irq, void 
> *dev_instance)
>               case BFIN_IPI_RESCHEDULE:
>                       /* That's the easiest one; leave it to
>                        * return_from_int. */
> +                     scheduler_ipi();
>                       kfree(msg);
>                       break;
>               case BFIN_IPI_CALL_FUNC:
> @@ -301,7 +302,7 @@ void smp_send_reschedule(int cpu)
>  
>       msg = kzalloc(sizeof(*msg), GFP_ATOMIC);
>       if (!msg)
> -             return;
> +             return; /* XXX unreliable needs fixing ! */
>       INIT_LIST_HEAD(&msg->list);
>       msg->type = BFIN_IPI_RESCHEDULE;
>  
> diff --git a/arch/cris/arch-v32/kernel/smp.c b/arch/cris/arch-v32/kernel/smp.c
> index 84fed3b..86e3c76 100644
> --- a/arch/cris/arch-v32/kernel/smp.c
> +++ b/arch/cris/arch-v32/kernel/smp.c
> @@ -340,15 +340,18 @@ irqreturn_t crisv32_ipi_interrupt(int irq, void *dev_id)
>  
>       ipi = REG_RD(intr_vect, irq_regs[smp_processor_id()], rw_ipi);
>  
> +     if (ipi.vector & IPI_SCHEDULE) {
> +             scheduler_ipi();
> +     }
>       if (ipi.vector & IPI_CALL) {
> -              func(info);
> +             func(info);
>       }
>       if (ipi.vector & IPI_FLUSH_TLB) {
> -                  if (flush_mm == FLUSH_ALL)
> -                      __flush_tlb_all();
> -                  else if (flush_vma == FLUSH_ALL)
> +             if (flush_mm == FLUSH_ALL)
> +                     __flush_tlb_all();
> +             else if (flush_vma == FLUSH_ALL)
>                       __flush_tlb_mm(flush_mm);
> -                  else
> +             else
>                       __flush_tlb_page(flush_vma, flush_addr);
>       }
>  
> diff --git a/arch/ia64/kernel/irq_ia64.c b/arch/ia64/kernel/irq_ia64.c
> index 9a26015..a580230 100644
> --- a/arch/ia64/kernel/irq_ia64.c
> +++ b/arch/ia64/kernel/irq_ia64.c
> @@ -31,6 +31,7 @@
>  #include <linux/irq.h>
>  #include <linux/ratelimit.h>
>  #include <linux/acpi.h>
> +#include <linux/sched.h>
>  
>  #include <asm/delay.h>
>  #include <asm/intrinsics.h>
> @@ -496,6 +497,7 @@ ia64_handle_irq (ia64_vector vector, struct pt_regs *regs)
>                       smp_local_flush_tlb();
>                       kstat_incr_irqs_this_cpu(irq, desc);
>               } else if (unlikely(IS_RESCHEDULE(vector))) {
> +                     scheduler_ipi();
>                       kstat_incr_irqs_this_cpu(irq, desc);
>               } else {
>                       ia64_setreg(_IA64_REG_CR_TPR, vector);
> diff --git a/arch/ia64/xen/irq_xen.c b/arch/ia64/xen/irq_xen.c
> index a3fb7cf..2f235a3 100644
> --- a/arch/ia64/xen/irq_xen.c
> +++ b/arch/ia64/xen/irq_xen.c
> @@ -92,6 +92,8 @@ static unsigned short saved_irq_cnt;
>  static int xen_slab_ready;
>  
>  #ifdef CONFIG_SMP
> +#include <linux/sched.h>
> +
>  /* Dummy stub. Though we may check XEN_RESCHEDULE_VECTOR before __do_IRQ,
>   * it ends up to issue several memory accesses upon percpu data and
>   * thus adds unnecessary traffic to other paths.
> @@ -99,7 +101,13 @@ static int xen_slab_ready;
>  static irqreturn_t
>  xen_dummy_handler(int irq, void *dev_id)
>  {
> +     return IRQ_HANDLED;
> +}
>  
> +static irqreturn_t
> +xen_resched_handler(int irq, void *dev_id)
> +{
> +     scheduler_ipi();
>       return IRQ_HANDLED;
>  }
>  
> @@ -110,7 +118,7 @@ static struct irqaction xen_ipi_irqaction = {
>  };
>  
>  static struct irqaction xen_resched_irqaction = {
> -     .handler =      xen_dummy_handler,
> +     .handler =      xen_resched_handler,
>       .flags =        IRQF_DISABLED,
>       .name =         "resched"
>  };
> diff --git a/arch/m32r/kernel/smp.c b/arch/m32r/kernel/smp.c
> index 31cef20..f0ecc3f 100644
> --- a/arch/m32r/kernel/smp.c
> +++ b/arch/m32r/kernel/smp.c
> @@ -138,7 +138,7 @@ void smp_send_reschedule(int cpu_id)
>   
> *==========================================================================*/
>  void smp_reschedule_interrupt(void)
>  {
> -     /* nothing to do */
> +     scheduler_ipi();
>  }
>  
>  /*==========================================================================*
> diff --git a/arch/mips/kernel/smtc.c b/arch/mips/kernel/smtc.c
> index 39c0825..0443e91 100644
> --- a/arch/mips/kernel/smtc.c
> +++ b/arch/mips/kernel/smtc.c
> @@ -931,6 +931,7 @@ static void post_direct_ipi(int cpu, struct smtc_ipi 
> *pipi)
>  static void ipi_resched_interrupt(void)
>  {
>       /* Return from interrupt should be enough to cause scheduler check */
> +     scheduler_ipi();
>  }
>  
>  static void ipi_call_interrupt(void)
> diff --git a/arch/mips/sibyte/bcm1480/smp.c b/arch/mips/sibyte/bcm1480/smp.c
> index 47b347c..513a301 100644
> --- a/arch/mips/sibyte/bcm1480/smp.c
> +++ b/arch/mips/sibyte/bcm1480/smp.c
> @@ -20,6 +20,7 @@
>  #include <linux/delay.h>
>  #include <linux/smp.h>
>  #include <linux/kernel_stat.h>
> +#include <linux/sched.h>
>  
>  #include <asm/mmu_context.h>
>  #include <asm/io.h>
> @@ -189,10 +190,8 @@ void bcm1480_mailbox_interrupt(void)
>       /* Clear the mailbox to clear the interrupt */
>       __raw_writeq(((u64)action)<<48, mailbox_0_clear_regs[cpu]);
>  
> -     /*
> -      * Nothing to do for SMP_RESCHEDULE_YOURSELF; returning from the
> -      * interrupt will do the reschedule for us
> -      */
> +     if (actione & SMP_RESCHEDULE_YOURSELF)
> +             scheduler_ipi();
>  
>       if (action & SMP_CALL_FUNCTION)
>               smp_call_function_interrupt();
> diff --git a/arch/mips/sibyte/sb1250/smp.c b/arch/mips/sibyte/sb1250/smp.c
> index c00a5cb..38e7f6b 100644
> --- a/arch/mips/sibyte/sb1250/smp.c
> +++ b/arch/mips/sibyte/sb1250/smp.c
> @@ -21,6 +21,7 @@
>  #include <linux/interrupt.h>
>  #include <linux/smp.h>
>  #include <linux/kernel_stat.h>
> +#include <linux/sched.h>
>  
>  #include <asm/mmu_context.h>
>  #include <asm/io.h>
> @@ -177,10 +178,8 @@ void sb1250_mailbox_interrupt(void)
>       /* Clear the mailbox to clear the interrupt */
>       ____raw_writeq(((u64)action) << 48, mailbox_clear_regs[cpu]);
>  
> -     /*
> -      * Nothing to do for SMP_RESCHEDULE_YOURSELF; returning from the
> -      * interrupt will do the reschedule for us
> -      */
> +     if (action & SMP_RESCHEDULE_YOURSELF)
> +             scheduler_ipi();
>  
>       if (action & SMP_CALL_FUNCTION)
>               smp_call_function_interrupt();
> diff --git a/arch/mn10300/kernel/smp.c b/arch/mn10300/kernel/smp.c
> index 0dcd1c6..17f16ca 100644
> --- a/arch/mn10300/kernel/smp.c
> +++ b/arch/mn10300/kernel/smp.c
> @@ -471,7 +471,7 @@ void smp_send_stop(void)
>   */
>  static irqreturn_t smp_reschedule_interrupt(int irq, void *dev_id)
>  {
> -     /* do nothing */
> +     scheduler_ipi();
>       return IRQ_HANDLED;
>  }
>  
> diff --git a/arch/parisc/kernel/smp.c b/arch/parisc/kernel/smp.c
> index 69d63d3..f8f7970 100644
> --- a/arch/parisc/kernel/smp.c
> +++ b/arch/parisc/kernel/smp.c
> @@ -155,6 +155,7 @@ ipi_interrupt(int irq, void *dev_id)
>                               
>                       case IPI_RESCHEDULE:
>                               smp_debug(100, KERN_DEBUG "CPU%d 
> IPI_RESCHEDULE\n", this_cpu);
> +                             scheduler_ipi();
>                               /*
>                                * Reschedule callback.  Everything to be
>                                * done is done by the interrupt return path.
> diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> index 68034bb..7ee0fc3 100644
> --- a/arch/powerpc/kernel/smp.c
> +++ b/arch/powerpc/kernel/smp.c
> @@ -128,6 +128,7 @@ static irqreturn_t call_function_action(int irq, void 
> *data)
>  static irqreturn_t reschedule_action(int irq, void *data)
>  {
>       /* we just need the return path side effect of checking need_resched */
> +     scheduler_ipi();
>       return IRQ_HANDLED;
>  }
>  
> diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
> index 94cf510..61789e8 100644
> --- a/arch/s390/kernel/smp.c
> +++ b/arch/s390/kernel/smp.c
> @@ -163,12 +163,12 @@ static void do_ext_call_interrupt(unsigned int 
> ext_int_code,
>  
>       /*
>        * handle bit signal external calls
> -      *
> -      * For the ec_schedule signal we have to do nothing. All the work
> -      * is done automatically when we return from the interrupt.
>        */
>       bits = xchg(&S390_lowcore.ext_call_fast, 0);
>  
> +     if (test_bit(ec_schedule, &bits))
> +             scheduler_ipi();
> +
>       if (test_bit(ec_call_function, &bits))
>               generic_smp_call_function_interrupt();
>  
> diff --git a/arch/sh/kernel/smp.c b/arch/sh/kernel/smp.c
> index 509b36b..6207561 100644
> --- a/arch/sh/kernel/smp.c
> +++ b/arch/sh/kernel/smp.c
> @@ -20,6 +20,7 @@
>  #include <linux/module.h>
>  #include <linux/cpu.h>
>  #include <linux/interrupt.h>
> +#include <linux/sched.h>
>  #include <asm/atomic.h>
>  #include <asm/processor.h>
>  #include <asm/system.h>
> @@ -323,6 +324,7 @@ void smp_message_recv(unsigned int msg)
>               generic_smp_call_function_interrupt();
>               break;
>       case SMP_MSG_RESCHEDULE:
> +             scheduler_ipi();
>               break;
>       case SMP_MSG_FUNCTION_SINGLE:
>               generic_smp_call_function_single_interrupt();
> diff --git a/arch/sparc/kernel/smp_32.c b/arch/sparc/kernel/smp_32.c
> index 91c10fb..042d8c9 100644
> --- a/arch/sparc/kernel/smp_32.c
> +++ b/arch/sparc/kernel/smp_32.c
> @@ -125,7 +125,7 @@ struct linux_prom_registers smp_penguin_ctable 
> __cpuinitdata = { 0 };
>  
>  void smp_send_reschedule(int cpu)
>  {
> -     /* See sparc64 */
> +     scheduler_ipi();
>  }
>  
>  void smp_send_stop(void)
> diff --git a/arch/sparc/kernel/smp_64.c b/arch/sparc/kernel/smp_64.c
> index b6a2b8f..68e26e2 100644
> --- a/arch/sparc/kernel/smp_64.c
> +++ b/arch/sparc/kernel/smp_64.c
> @@ -1369,6 +1369,7 @@ void smp_send_reschedule(int cpu)
>  void __irq_entry smp_receive_signal_client(int irq, struct pt_regs *regs)
>  {
>       clear_softint(1 << irq);
> +     scheduler_ipi();
>  }
>  
>  /* This is a nop because we capture all other cpus
> diff --git a/arch/tile/kernel/smp.c b/arch/tile/kernel/smp.c
> index 9575b37..91a1ddf 100644
> --- a/arch/tile/kernel/smp.c
> +++ b/arch/tile/kernel/smp.c
> @@ -190,6 +190,7 @@ static irqreturn_t handle_reschedule_ipi(int irq, void 
> *token)
>        * profiler count in the meantime.
>        */
>       __get_cpu_var(irq_stat).irq_resched_count++;
> +     scheduler_ipi();
>  
>       return IRQ_HANDLED;
>  }
> diff --git a/arch/um/kernel/smp.c b/arch/um/kernel/smp.c
> index 106bf27..eefb107 100644
> --- a/arch/um/kernel/smp.c
> +++ b/arch/um/kernel/smp.c
> @@ -173,7 +173,7 @@ void IPI_handler(int cpu)
>                       break;
>  
>               case 'R':
> -                     set_tsk_need_resched(current);
> +                     scheduler_ipi();
>                       break;
>  
>               case 'S':
> diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
> index 513deac..e38c2d8 100644
> --- a/arch/x86/kernel/smp.c
> +++ b/arch/x86/kernel/smp.c
> @@ -202,6 +202,7 @@ void smp_reschedule_interrupt(struct pt_regs *regs)
>  {
>       ack_APIC_irq();
>       inc_irq_stat(irq_resched_count);
> +     scheduler_ipi();
>       /*
>        * KVM uses this interrupt to force a cpu out of guest mode
>        */
> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> index 72a4c79..6196fb1 100644
> --- a/arch/x86/xen/smp.c
> +++ b/arch/x86/xen/smp.c
> @@ -53,6 +53,7 @@ static irqreturn_t xen_call_function_single_interrupt(int 
> irq, void *dev_id);
>  static irqreturn_t xen_reschedule_interrupt(int irq, void *dev_id)
>  {
>       inc_irq_stat(irq_resched_count);
> +     scheduler_ipi();
>  
>       return IRQ_HANDLED;
>  }
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 341acbb..aa458dc 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2183,6 +2183,7 @@ extern void set_task_comm(struct task_struct *tsk, char 
> *from);
>  extern char *get_task_comm(char *to, struct task_struct *tsk);
>  
>  #ifdef CONFIG_SMP
> +static inline void scheduler_ipi(void) { }
>  extern unsigned long wait_task_inactive(struct task_struct *, long 
> match_state);
>  #else
>  static inline unsigned long wait_task_inactive(struct task_struct *p,



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