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

Wed Jul 6 07:18:42 EDT 2011

On 06/07/11 12:11, Russell King - ARM Linux wrote:
> 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.

Note that this mandates SPARSE_IRQ, so the number of allocated irq
structures is actually very limited (most platforms only allocate 3
structures per CPU for PPI #29, 30 and 31).

> 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.

Fair enough, I have no problem with you merging it once you're happy
with it.

Cheers,

	M.
-- 
Jazz is not dead. It just smells funny...