[PATCH v8 00/14] Consolidating GIC per-cpu interrupts

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Wed, Jul 06, 2011 at 12:02:26PM +0100, Marc Zyngier wrote:
> On 05/07/11 09:49, Marc Zyngier wrote:
> > The current GIC per-cpu interrupts (aka PPIs) suffer from a number of
> > problems:
> > 
> > - They use a completely separate scheme to handle the interrupts,
> >   mostly because the PPI concept doesn't really match the kernel view
> >   of an interrupt.
> > - PPIs can only be used by the timer code, unless we add more low-level
> >   assembly code.
> > - The local timer code can only be used by devices generating PPIs,
> >   and not SPIs.
> > - At least one platform (msm) has started implementing its own
> >   alternative scheme.
> > - Some low-level code gets duplicated, as usual...
> > 
> > The proposed solution is to let the GIC code expose the PPIs as
> > something that the kernel can manage. Instead of having a single
> > interrupt number shared on all cores, make the interrupt number be
> > different on each CPU.
> > 
> > This enables the use of the normal kernel API (request_irq() and
> > friends) and the elimination of some low level code. It also serves as
> > the basis of the GIC device tree support code. On the other side, it
> > causes quite a bit of churn in the timer code.
> > 
> > Previous versions of this series have received ACKs from some platform
> > maintainers, but so far there has been very little comment on the core
> > code. As I now have quite a large number of patches relying on this
> > series (local timers as devices, device tree support for GIC and TWD),
> > I'd be grateful for at least a hint indicating that this is going in
> > the right direction. Or not.
> > 
> > This patch set is based on 3.0-rc5. Tested on PB-11MP, Tegra2
> > (Harmony) and SMDK-V310. Also available in the "gic_ppi_map" branch of
> > git://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git
> > 
> > From v7:
> > - Rebased on v3.0-rc5
> > - Rename gic_ppi_to_vppi() to gic_ppi_map()
> > - Rename CONFIG_ARM_GIC_VPPI to CONFIG_ARM_GIC_PPI_MAP
> > - Add gic_ppi_map_on_cpu()
> > 
> > From v6:
> > - Fix compilation when !CONFIG_PM.
> > 
> > From v5:
> > - Update Exynos4 MCT to use the local timer infrastructure, now that
> >   it doesn't depend on PPIs anymore. Untested, as the board I have
> >   doesn't implement MCT (EVT0 syndrome).
> > 
> > From v4:
> > - Fix arch/arm/common/Kconfig indentation
> > - Fix MSM warning when building UP.
> > 
> > From v3:
> > - Fix yet another CPU_HOTPLUG problem: instead of calling free_irq()
> >   on timer halt, just disable the interrupt. On timer restart, detect
> >   that the interrupt has been requested already and just enable the
> >   interrupt back. This avoid doing a request_irq() with preemption
> >   disabled, which triggers an ugly warning. Reported by Stephen Boyd.
> > 
> > From v2:
> > - More MSM fixes
> > - Dropped MSM interrupt handler removal, as this requires more discussion,
> >   and will be addressed in a separate series.
> > - Moved introduction of percpu_timer_handler to a separate patch
> > 
> > From v1:
> > - Fix crash while hotpluging a CPU
> > - Use handle_percpu_irq() instead of handle_fasteoi_irq()
> > - MSM fixes courtesy of Stephen Boyd
> > - MSM switched to percpu_timer_handler()
> > - Remove local timer interrupt accounting
> > - Restructure patches #1 and #2
> > 
> > Marc Zyngier (14):
> >   ARM: gic: add per-cpu interrupt mapping
> >   ARM: smp: add interrupt handler for local timers
> >   ARM: smp_twd: add support for remapped PPI interrupts
> >   ARM: omap4: use remapped PPI interrupts for local timer
> >   ARM: versatile: use remapped PPI interrupts for local timer
> >   ARM: shmobile: use remapped PPI interrupts for local timer
> >   ARM: ux500: use remapped PPI interrupts for local timer
> >   ARM: tegra: use remapped PPI interrupts for local timer
> >   ARM: msm: use remapped PPI interrupts for local timer
> >   ARM: exynos4: use remapped PPI interrupts for local timer
> >   ARM: gic: remove previous local timer interrupt handling
> >   ARM: gic: add compute_irqnr macro for exynos4
> >   ARM: SMP: automatically select ARM_GIC_PPI_MAP
> >   ARM: gic: add gic_ppi_map_on_cpu()
> > 
> >  arch/arm/Kconfig                                  |    1 +
> >  arch/arm/common/Kconfig                           |    5 +
> >  arch/arm/common/gic.c                             |  152 +++++++++++++++++++--
> >  arch/arm/include/asm/entry-macro-multi.S          |    7 -
> >  arch/arm/include/asm/hardirq.h                    |    3 -
> >  arch/arm/include/asm/hardware/entry-macro-gic.S   |   31 ++---
> >  arch/arm/include/asm/hardware/gic.h               |   11 ++-
> >  arch/arm/include/asm/localtimer.h                 |    7 +-
> >  arch/arm/include/asm/smp.h                        |    5 -
> >  arch/arm/kernel/irq.c                             |   11 +-
> >  arch/arm/kernel/smp.c                             |   27 +---
> >  arch/arm/kernel/smp_twd.c                         |   25 +++-
> >  arch/arm/mach-exynos4/include/mach/entry-macro.S  |   70 +---------
> >  arch/arm/mach-exynos4/localtimer.c                |    3 +-
> >  arch/arm/mach-msm/board-msm8x60.c                 |   11 --
> >  arch/arm/mach-msm/include/mach/entry-macro-qgic.S |   73 +----------
> >  arch/arm/mach-msm/timer.c                         |   58 ++++----
> >  arch/arm/mach-omap2/include/mach/entry-macro.S    |   14 +--
> >  arch/arm/mach-omap2/timer-mpu.c                   |    3 +-
> >  arch/arm/mach-shmobile/entry-intc.S               |    3 -
> >  arch/arm/mach-shmobile/include/mach/entry-macro.S |    3 -
> >  arch/arm/mach-shmobile/localtimer.c               |    3 +-
> >  arch/arm/mach-tegra/localtimer.c                  |    3 +-
> >  arch/arm/mach-ux500/localtimer.c                  |    3 +-
> >  arch/arm/plat-versatile/localtimer.c              |    3 +-
> >  25 files changed, 253 insertions(+), 282 deletions(-)
> 
> Russell,
> 
> Unless you have any objection, I'd like to push this to Arnd's arm-soc
> tree. Would that be OK with you?

I've yet to look at any of these patches in any depth - my immediate
concern is gobbling up soo many IRQ numbers for the per-cpu stuff
(which also eats up memory for all the irq structures) when this
isn't really necessary.

Plus is this patch set core stuff or SoC stuff?  It looks more core
to me, so that means it should come through my tree rather than
Arnd's.