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    SubjectRe: [patch] genapic: default to physical mode on hotplug CPU kernels

    * Siddha, Suresh B <suresh.b.siddha@intel.com> wrote:

    > On Tue, Nov 28, 2006 at 09:23:22PM +0100, Ingo Molnar wrote:
    > >
    > > * Siddha, Suresh B <suresh.b.siddha@intel.com> wrote:
    > >
    > > > On Tue, Nov 28, 2006 at 07:33:46AM +0100, Ingo Molnar wrote:
    > > > > - if (clusters <= 1 && max_cluster <= 8 && cluster_cnt[0] == max_cluster)
    > > > > + if (max_apic < 8)
    > > >
    > > > Patch mostly looks good. Instead of checking for max_apic, can we use
    > > > cpus_weight(cpu_possible_map) <= 8
    > >
    > > ok - but i think it's still possible the BIOS tells us APIC IDs that are
    > > larger than 7, even if there are fewer CPUs. So i think the patch below
    > > should cover it. Agreed?
    > >
    >
    > I think it is ok to use flat mode even when APIC IDs are larger than
    > 7, as we rely on LDR's which are programmed using smp_processor_id().
    >
    > IMO, cpus_weight check should be fine.

    hm - indeed. Then we can indeed do the patch below. Nice simplification!

    Ingo

    -------------------->
    From: Ingo Molnar <mingo@elte.hu>
    Subject: [patch] genapic: default to physical mode on hotplug CPU kernels

    default to physical mode on hotplug CPU kernels. Furher simplify and
    clean up the APIC initialization code.

    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    ---
    arch/x86_64/kernel/genapic.c | 20 +++-----------------
    arch/x86_64/kernel/mpparse.c | 2 +-
    include/asm-x86_64/apic.h | 2 +-
    3 files changed, 5 insertions(+), 19 deletions(-)

    Index: linux/arch/x86_64/kernel/genapic.c
    ===================================================================
    --- linux.orig/arch/x86_64/kernel/genapic.c
    +++ linux/arch/x86_64/kernel/genapic.c
    @@ -33,25 +33,11 @@ u8 x86_cpu_to_log_apicid[NR_CPUS] = { [0
    struct genapic __read_mostly *genapic = &apic_flat;

    /*
    - * Check the APIC IDs in bios_cpu_apicid and choose the APIC mode.
    + * Choose the APIC routing mode:
    */
    -void __init clustered_apic_check(void)
    +void __init setup_apic_routing(void)
    {
    - unsigned int i, max_apic = 0;
    - u8 id;
    -
    - /*
    - * Determine the maximum APIC ID in use:
    - */
    - for (i = 0; i < NR_CPUS; i++) {
    - id = bios_cpu_apicid[i];
    - if (id == BAD_APICID)
    - continue;
    - if (id > max_apic)
    - max_apic = id;
    - }
    -
    - if (max_apic < 8)
    + if (cpus_weight(cpu_possible_map) <= 8)
    genapic = &apic_flat;
    else
    genapic = &apic_physflat;
    Index: linux/arch/x86_64/kernel/mpparse.c
    ===================================================================
    --- linux.orig/arch/x86_64/kernel/mpparse.c
    +++ linux/arch/x86_64/kernel/mpparse.c
    @@ -302,7 +302,7 @@ static int __init smp_read_mpc(struct mp
    }
    }
    }
    - clustered_apic_check();
    + setup_apic_routing();
    if (!num_processors)
    printk(KERN_ERR "MPTABLE: no processors registered!\n");
    return num_processors;
    Index: linux/include/asm-x86_64/apic.h
    ===================================================================
    --- linux.orig/include/asm-x86_64/apic.h
    +++ linux/include/asm-x86_64/apic.h
    @@ -82,7 +82,7 @@ extern void setup_secondary_APIC_clock (
    extern int APIC_init_uniprocessor (void);
    extern void disable_APIC_timer(void);
    extern void enable_APIC_timer(void);
    -extern void clustered_apic_check(void);
    +extern void setup_apic_routing(void);
    static inline void lapic_timer_idle_broadcast(int broadcast) { }

    extern void setup_APIC_extened_lvt(unsigned char lvt_off, unsigned char vector,
    -
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