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Message-ID: <1438636720.2097.63.camel@freescale.com>
Date: Mon, 3 Aug 2015 16:18:40 -0500
From: Scott Wood <scottwood@...escale.com>
To: Chenhui Zhao <chenhui.zhao@...escale.com>
CC: <b29983@...escale.com>, <b07421@...escale.com>,
<linux-kernel@...r.kernel.org>,
Tang Yuantian <Yuantian.Tang@...escale.com>,
<linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 2/3] PowerPC/mpc85xx: Add hotplug support on E5500 and
E500MC cores
[Added linuxppc-dev@...ts.ozlabs.org. Besides that list being required for
review of PPC patches, it feeds the patchwork that I use to track and apply
patches.]
On Mon, 2015-08-03 at 19:52 +0800, Chenhui Zhao wrote:
> On Sat, Aug 1, 2015 at 8:14 AM, Scott Wood <scottwood@...escale.com>
> wrote:
> > On Fri, 2015-07-31 at 17:20 +0800, b29983@...escale.comwrote:
> > > From: Tang Yuantian <Yuantian.Tang@...escale.com>
> > >
> > > Freescale E500MC and E5500 core-based platforms, like P4080, T1040,
> > > support disabling/enabling CPU dynamically.
> > > This patch adds this feature on those platforms.
> > >
> > > Signed-off-by: Chenhui Zhao <chenhui.zhao@...escale.com>
> > > Signed-off-by: Tang Yuantian <Yuantian.Tang@...scale.com>
> > > ---
> > > arch/powerpc/Kconfig | 2 +-
> > > arch/powerpc/include/asm/smp.h | 1 +
> > > arch/powerpc/kernel/smp.c | 5 +++++
> > > arch/powerpc/platforms/85xx/smp.c | 39
> > > ++++++++++++++++++++++++++++++++----
> > > ---
> > > 4 files changed, 39 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > > index 5ef2711..dd9e252 100644
> > > --- a/arch/powerpc/Kconfig
> > > +++ b/arch/powerpc/Kconfig
> > > @@ -386,7 +386,7 @@ config SWIOTLB
> > > config HOTPLUG_CPU
> > > bool "Support for enabling/disabling CPUs"
> > > depends on SMP && (PPC_PSERIES || \
> > > - PPC_PMAC || PPC_POWERNV || (PPC_85xx && !PPC_E500MC))
> > > + PPC_PMAC || PPC_POWERNV || FSL_SOC_BOOKE)
> > > ---help---
> > > Say Y here to be able to disable and re-enable individual
> > > CPUs at runtime on SMP machines.
> >
> >
> >
> > > diff --git a/arch/powerpc/include/asm/smp.h
> > > b/arch/powerpc/include/asm/smp.h
> > > index 825663c..bf37d17 100644
> > > --- a/arch/powerpc/include/asm/smp.h
> > > +++ b/arch/powerpc/include/asm/smp.h
> > > @@ -67,6 +67,7 @@ void generic_cpu_die(unsigned int cpu);
> > > void generic_set_cpu_dead(unsigned int cpu);
> > > void generic_set_cpu_up(unsigned int cpu);
> > > int generic_check_cpu_restart(unsigned int cpu);
> > > +int generic_check_cpu_dead(unsigned int cpu);
> > > #endif
> > >
> > > #ifdef CONFIG_PPC64
> > > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> > > index ec9ec20..2cca27a 100644
> > > --- a/arch/powerpc/kernel/smp.c
> > > +++ b/arch/powerpc/kernel/smp.c
> > > @@ -454,6 +454,11 @@ int generic_check_cpu_restart(unsigned int cpu)
> > > return per_cpu(cpu_state, cpu) == CPU_UP_PREPARE;
> > > }
> > >
> > > +int generic_check_cpu_dead(unsigned int cpu)
> > > +{
> > > + return per_cpu(cpu_state, cpu) == CPU_DEAD;
> > > +}
> >
> > Is there a non-generic check_cpu_dead()?
>
> NO, just follow the name "generic_check_cpu_restart()".
But it's not the same situation as generic_check_cpu_restart().
> > It gets open-coded in generic_cpu_die()... Either open-code it
> > elsewhere, or
> > call it check_cpu_dead() and use it everywhere there's a CPU_DEAD
> > check.
> >
> >
> > > +
> > > static bool secondaries_inhibited(void)
> > > {
> > > return kvm_hv_mode_active();
> > > diff --git a/arch/powerpc/platforms/85xx/smp.c
> > > b/arch/powerpc/platforms/85xx/smp.c
> > > index 6811a5b..7f0dadb 100644
> > > --- a/arch/powerpc/platforms/85xx/smp.c
> > > +++ b/arch/powerpc/platforms/85xx/smp.c
> > > @@ -42,6 +42,7 @@ struct epapr_spin_table {
> > > u32 pir;
> > > };
> > >
> > > +#ifdef CONFIG_HOTPLUG_CPU
> > > static u64 timebase;
> > > static int tb_req;
> > > static int tb_valid;
> > > @@ -111,7 +112,7 @@ static void mpc85xx_take_timebase(void)
> > > local_irq_restore(flags);
> > > }
> > >
> > > -#ifdef CONFIG_HOTPLUG_CPU
> > > +#ifndef CONFIG_PPC_E500MC
> > > static void e500_cpu_idle(void)
> >
> > What happens if we bisect to patch 1/3 and run this on e500mc?
> >
> > Please move the ifdef to that patch.
>
> OK.
>
> >
> >
> > > {
> > > u32 tmp;
> > > @@ -127,6 +128,7 @@ static void e500_cpu_idle(void)
> > > mtmsr(tmp);
> > > isync();
> > > }
> > > +#endif
> > >
> > > static void qoriq_cpu_dying(void)
> > > {
> > > @@ -144,11 +146,30 @@ static void qoriq_cpu_dying(void)
> > >
> > > generic_set_cpu_dead(cpu);
> > >
> > > +#ifndef CONFIG_PPC_E500MC
> > > e500_cpu_idle();
> > > +#endif
> > >
> > > while (1)
> > > ;
> > > }
> > > +
> > > +static void qoriq_real_cpu_die(unsigned int cpu)
> >
> > Real as opposed to...?
>
> It's hard to find a good name. :)
There are too many cpu_die() functions as is, and adding cpu_dying makes it
worse. Even just trying to come up with suggestions I've been having a hard
time keeping track of which one goes in which ops struct. This problem goes
beyond the 85xx code, to the ridiculous and undocumented distinction between
cpu_die() and __cpu_die().
It wouldn't be so bad if each layer were self contained, rather than multiple
layers being defined in the same file. I suggest keeping the existing
convention whereby ppc_md.cpu_die ends in "_mach_cpu_die". Don't call
anything "cpu_dying".
I'd call qoriq_pm_ops->cpu_die something else (e.g. cpu_kill) even though it
is in a separate file, just because of how confused and overused the name is
elsewhere.
> +{
> > > + int i;
> > > +
> > > + for (i = 0; i < 50000; i++) {
> > > + if (generic_check_cpu_dead(cpu)) {
> > > + qoriq_pm_ops->cpu_die(cpu);
> > > +#ifdef CONFIG_PPC64
> > > + paca[cpu].cpu_start = 0;
> > > +#endif
> > > + return;
> > > + }
> > > + udelay(10);
> > > + }
> > > + pr_err("%s: CPU%d didn't die...\n", __func__, cpu);
> > > +}
> >
> > Only 500ms timeout, versus 10sec in generic_cpu_die()?
>
> The process is fast. Maybe 10 second is too large.
Is it fast 100% of the time? What if the CPU you intend to die is in a long
critical section? What harm is there to having a longer timeout, similar to
what other platforms use?
>
> >
> > > #endif
> > >
> > > static inline void flush_spin_table(void *spin_table)
> > > @@ -246,11 +267,7 @@ static int smp_85xx_kick_cpu(int nr)
> > > spin_table = phys_to_virt(*cpu_rel_addr);
> > >
> > > local_irq_save(flags);
> > > -#ifdef CONFIG_PPC32
> > > #ifdef CONFIG_HOTPLUG_CPU
> > > - /* Corresponding to generic_set_cpu_dead() */
> > > - generic_set_cpu_up(nr);
> > > -
> > > if (system_state == SYSTEM_RUNNING) {
> > > /*
> > > * To keep it compatible with old boot program which
> > > uses
> > > @@ -263,6 +280,7 @@ static int smp_85xx_kick_cpu(int nr)
> > > out_be32(&spin_table->addr_l, 0);
> > > flush_spin_table(spin_table);
> > >
> > > + qoriq_pm_ops->cpu_up(nr);
> >
> > Again, is it possible to get here without a valid qoriq_pm_ops (i.e.
> > is there
> > anything stopping the user from trying to initiate CPU hotplug)?
> >
> > -Scott
>
> For every platform running this code, should has a valid qoriq_pm_ops.
> If not valid, it's a bug.
How do you prevent this code from running when there is no valid qoriq_pm_ops?
-Scott
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