13 Jan, 2012

1 commit


03 Oct, 2011

1 commit

  • The ARM GIC interrupt controller offers per CPU interrupts (PPIs),
    which are usually used to connect local timers to each core. Each CPU
    has its own private interface to the GIC, and only sees the PPIs that
    are directly connect to it.

    While these timers are separate devices and have a separate interrupt
    line to a core, they all use the same IRQ number.

    For these devices, request_irq() is not the right API as it assumes
    that an IRQ number is visible by a number of CPUs (through the
    affinity setting), but makes it very awkward to express that an IRQ
    number can be handled by all CPUs, and yet be a different interrupt
    line on each CPU, requiring a different dev_id cookie to be passed
    back to the handler.

    The *_percpu_irq() functions is designed to overcome these
    limitations, by providing a per-cpu dev_id vector:

    int request_percpu_irq(unsigned int irq, irq_handler_t handler,
    const char *devname, void __percpu *percpu_dev_id);
    void free_percpu_irq(unsigned int, void __percpu *);
    int setup_percpu_irq(unsigned int irq, struct irqaction *new);
    void remove_percpu_irq(unsigned int irq, struct irqaction *act);
    void enable_percpu_irq(unsigned int irq);
    void disable_percpu_irq(unsigned int irq);

    The API has a number of limitations:
    - no interrupt sharing
    - no threading
    - common handler across all the CPUs

    Once the interrupt is requested using setup_percpu_irq() or
    request_percpu_irq(), it must be enabled by each core that wishes its
    local interrupt to be delivered.

    Based on an initial patch by Thomas Gleixner.

    Signed-off-by: Marc Zyngier
    Cc: linux-arm-kernel@lists.infradead.org
    Link: http://lkml.kernel.org/r/1316793788-14500-2-git-send-email-marc.zyngier@arm.com
    Signed-off-by: Thomas Gleixner

    Marc Zyngier
     

29 Mar, 2011

1 commit


28 Mar, 2011

1 commit


26 Feb, 2011

1 commit

  • Add a commandline parameter "threadirqs" which forces all interrupts except
    those marked IRQF_NO_THREAD to run threaded. That's mostly a debug option to
    allow retrieving better debug data from crashing interrupt handlers. If
    "threadirqs" is not enabled on the kernel command line, then there is no
    impact in the interrupt hotpath.

    Architecture code needs to select CONFIG_IRQ_FORCED_THREADING after
    marking the interrupts which cant be threaded IRQF_NO_THREAD. All
    interrupts which have IRQF_TIMER set are implict marked
    IRQF_NO_THREAD. Also all PER_CPU interrupts are excluded.

    Forced threading hard interrupts also forces all soft interrupt
    handling into thread context.

    When enabled it might slow down things a bit, but for debugging problems in
    interrupt code it's a reasonable penalty as it does not immediately
    crash and burn the machine when an interrupt handler is buggy.

    Some test results on a Core2Duo machine:

    Cache cold run of:
    # time git grep irq_desc

    non-threaded threaded
    real 1m18.741s 1m19.061s
    user 0m1.874s 0m1.757s
    sys 0m5.843s 0m5.427s

    # iperf -c server
    non-threaded
    [ 3] 0.0-10.0 sec 1.09 GBytes 933 Mbits/sec
    [ 3] 0.0-10.0 sec 1.09 GBytes 934 Mbits/sec
    [ 3] 0.0-10.0 sec 1.09 GBytes 933 Mbits/sec
    threaded
    [ 3] 0.0-10.0 sec 1.09 GBytes 939 Mbits/sec
    [ 3] 0.0-10.0 sec 1.09 GBytes 934 Mbits/sec
    [ 3] 0.0-10.0 sec 1.09 GBytes 937 Mbits/sec

    Signed-off-by: Thomas Gleixner
    Cc: Peter Zijlstra
    LKML-Reference:

    Thomas Gleixner
     

19 Feb, 2011

30 commits


12 Oct, 2010

4 commits


04 Oct, 2010

1 commit