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    SubjectRe: [RFC -tip] x86: do_IRQ - send APIC EOI for x86-32 on irq without handler v3
    [Ingo Molnar - Fri, Apr 10, 2009 at 04:00:23PM +0200]
    |
    | * Cyrill Gorcunov <gorcunov@gmail.com> wrote:
    |
    | > [Ingo Molnar - Fri, Apr 10, 2009 at 02:27:50PM +0200]
    | > |
    | > | * Cyrill Gorcunov <gorcunov@openvz.org> wrote:
    | > |
    | > | > Ingo, I've checked the sources and as far as I see
    | > | > we could NOP'ify apic->write indeed but I have
    | > | > an internal feeling that this will bring us more problem
    | > | > in future (for example it could be the following scenario:
    | > | > some screwed APIC would require cleaning of LVT's or
    | > | > IRR after resume regardless if it was initialized
    | > | > or not at all). Mostly I mean that the idea of making
    | > | > apic->write NOP'ified is quite elegant indeed but
    | > | > cut off the subset of apic operations (we need
    | > | > apic->read anyway) somehow bothering me from inside :)
    | > |
    | > | it's as if assigned a special type of 'dummy apic' struct apic. It
    | > | wont cause problems down the line: we use the new APIC driver
    | > | infrastructure to abstract out quirks.
    | >
    | > Well, it's not that new actually :-)
    |
    | Yeah, i mean the new unified/modernized code in 2.6.30-to-be.
    |
    | > |
    | > | one small detail:
    | > |
    | > | > +/* Ack APIC irq if it's enabled only */
    | > | > +static inline void ack_APIC_irq_safe(void)
    | > | > +{
    | > | > +#ifdef CONFIG_X86_LOCAL_APIC
    | > | > + if (cpu_has_apic)
    | > | > + ack_APIC_irq();
    | > | > +#endif
    | > |
    | > | we dont need the cpu_has_apic check there, do we? In the
    | > | !cpu_has_apic the ->write method should be a dummy.
    | >
    | > Yes. In case you're talking about it'll not be needed
    | > (we will find earlier whether cpu_has_apic or not).
    |
    | yeah.
    |
    | Ingo
    |

    Ingo,

    I think you meant something like the patch below. It's
    not finished yet -- I need to find out right place for
    calling freshly introduced apic_disable_write_op.
    Will continue tomorrow.

    But even having it not completed yet I would like to
    get some feedbackabout code structure in general.

    Cyrill
    ---
    arch/x86/include/asm/apic.h | 10 ++++++++++
    arch/x86/kernel/apic/apic.c | 6 ++++++
    arch/x86/kernel/irq.c | 10 ++--------
    3 files changed, 18 insertions(+), 8 deletions(-)

    Index: linux-2.6.git/arch/x86/include/asm/apic.h
    =====================================================================
    --- linux-2.6.git.orig/arch/x86/include/asm/apic.h
    +++ linux-2.6.git/arch/x86/include/asm/apic.h
    @@ -106,6 +106,7 @@ extern void native_apic_wait_icr_idle(vo
    extern u32 native_safe_apic_wait_icr_idle(void);
    extern void native_apic_icr_write(u32 low, u32 id);
    extern u64 native_apic_icr_read(void);
    +extern void native_apic_write_dummy(u32 reg, u32 v);

    #define EIM_8BIT_APIC_ID 0
    #define EIM_32BIT_APIC_ID 1
    @@ -372,6 +373,15 @@ static inline void apic_write(u32 reg, u
    apic->write(reg, val);
    }

    +/*
    + * right after this call apic->write doesn't do anything
    + * note that there is no restore operation it works one way
    + */
    +static inline void apic_disable_write_op(void)
    +{
    + apic->write = native_apic_write_dummy;
    +}
    +
    static inline u64 apic_icr_read(void)
    {
    return apic->icr_read();
    Index: linux-2.6.git/arch/x86/kernel/apic/apic.c
    =====================================================================
    --- linux-2.6.git.orig/arch/x86/kernel/apic/apic.c
    +++ linux-2.6.git/arch/x86/kernel/apic/apic.c
    @@ -210,6 +210,12 @@ static int modern_apic(void)
    return lapic_get_version() >= 0x14;
    }

    +/*
    + * bare function to substitute write operation
    + * and it's _that_ fast :)
    + */
    +void native_apic_write_dummy(u32 reg, u32 v) { }
    +
    void native_apic_wait_icr_idle(void)
    {
    while (apic_read(APIC_ICR) & APIC_ICR_BUSY)
    Index: linux-2.6.git/arch/x86/kernel/irq.c
    =====================================================================
    --- linux-2.6.git.orig/arch/x86/kernel/irq.c
    +++ linux-2.6.git/arch/x86/kernel/irq.c
    @@ -27,7 +27,6 @@ void ack_bad_irq(unsigned int irq)
    if (printk_ratelimit())
    pr_err("unexpected IRQ trap at vector %02x\n", irq);

    -#ifdef CONFIG_X86_LOCAL_APIC
    /*
    * Currently unexpected vectors happen only on SMP and APIC.
    * We _must_ ack these because every local APIC has only N
    @@ -37,9 +36,7 @@ void ack_bad_irq(unsigned int irq)
    * completely.
    * But only ack when the APIC is enabled -AK
    */
    - if (cpu_has_apic)
    - ack_APIC_irq();
    -#endif
    + ack_APIC_irq();
    }

    #define irq_stats(x) (&per_cpu(irq_stat, x))
    @@ -224,10 +221,7 @@ unsigned int __irq_entry do_IRQ(struct p
    irq = __get_cpu_var(vector_irq)[vector];

    if (!handle_irq(irq, regs)) {
    -#ifdef CONFIG_X86_64
    - if (!disable_apic)
    - ack_APIC_irq();
    -#endif
    + ack_APIC_irq();

    if (printk_ratelimit())
    pr_emerg("%s: %d.%d No irq handler for vector (irq %d)\n",

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