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    SubjectRe: [rfc][patch 1/3] mm: vmap rewrite
    > After:
    > 78406 total 0.0081
    > 40053 default_idle 89.4040
    > 33576 ia64_spinlock_contention 349.7500
    > 1650 _spin_lock 17.1875

    Here is a patch that will unroll those two sample and let you see which
    function is hitting the contention. This has been submitted and
    rejected at least once a few years ago. I keep and old copy around
    because it is often very handy.

    I have not tested it in a couple years (usually working on performance with
    a SLES kernel). It applied with a couple minor fixups so I assume it
    works. If not, please let me know.



    Index: ia64_spinlock_contention/arch/ia64/kernel/head.S
    ===================================================================
    --- ia64_spinlock_contention.orig/arch/ia64/kernel/head.S 2008-07-28 17:35:21.000000000 -0500
    +++ ia64_spinlock_contention/arch/ia64/kernel/head.S 2008-07-28 17:35:51.000000000 -0500
    @@ -1137,6 +1137,8 @@ GLOBAL_ENTRY(ia64_spinlock_contention_pr
    tbit.nz p15,p0=r27,IA64_PSR_I_BIT
    .restore sp // pop existing prologue after next insn
    mov b6 = r28
    + .global ia64_spinlock_contention_pre3_4_beg // for kernprof
    +ia64_spinlock_contention_pre3_4_beg:
    .prologue
    .save ar.pfs, r0
    .altrp b6
    @@ -1185,6 +1187,8 @@ GLOBAL_ENTRY(ia64_spinlock_contention)
    (p14) br.cond.sptk.few .wait

    br.ret.sptk.many b6 // lock is now taken
    + .global ia64_spinlock_contention_end // for determining if we are in ia64_spinlock_contention code.
    +ia64_spinlock_contention_end:
    END(ia64_spinlock_contention)

    #endif
    Index: ia64_spinlock_contention/arch/ia64/kernel/ia64_ksyms.c
    ===================================================================
    --- ia64_spinlock_contention.orig/arch/ia64/kernel/ia64_ksyms.c 2008-07-28 17:35:21.000000000 -0500
    +++ ia64_spinlock_contention/arch/ia64/kernel/ia64_ksyms.c 2008-07-28 17:35:51.000000000 -0500
    @@ -95,6 +95,10 @@ EXPORT_SYMBOL(unw_init_running);
    */
    extern char ia64_spinlock_contention_pre3_4;
    EXPORT_SYMBOL(ia64_spinlock_contention_pre3_4);
    +extern char ia64_spinlock_contention_pre3_4_beg;
    +EXPORT_SYMBOL(ia64_spinlock_contention_pre3_4_beg);
    +extern char ia64_spinlock_contention_pre3_4_end;
    +EXPORT_SYMBOL(ia64_spinlock_contention_pre3_4_end);
    # else
    /*
    * This is not a normal routine and we don't want a function descriptor for it, so we use
    @@ -102,6 +106,8 @@ EXPORT_SYMBOL(ia64_spinlock_contention_p
    */
    extern char ia64_spinlock_contention;
    EXPORT_SYMBOL(ia64_spinlock_contention);
    +extern char ia64_spinlock_contention_end;
    +EXPORT_SYMBOL(ia64_spinlock_contention_end);
    # endif
    # endif
    #endif
    Index: ia64_spinlock_contention/arch/ia64/kernel/perfmon_default_smpl.c
    ===================================================================
    --- ia64_spinlock_contention.orig/arch/ia64/kernel/perfmon_default_smpl.c 2008-07-28 17:35:21.000000000 -0500
    +++ ia64_spinlock_contention/arch/ia64/kernel/perfmon_default_smpl.c 2008-07-28 18:18:56.000000000 -0500
    @@ -11,6 +11,7 @@
    #include <linux/init.h>
    #include <asm/delay.h>
    #include <linux/smp.h>
    +#include <linux/spinlock.h>

    #include <asm/perfmon.h>
    #include <asm/perfmon_default_smpl.h>
    @@ -98,6 +99,16 @@ default_init(struct task_struct *task, v
    return 0;
    }

    +#ifdef CONFIG_SMP
    +#if __GNUC__ < 3 || (__GNUC__ == 3 && __GNUC_MINOR__ < 3)
    +extern char ia64_spinlock_contention_pre3_4_beg[], ia64_spinlock_contention_pre3_4_end[];
    +#define ia64_spinlock_contention ia64_spinlock_contention_pre3_4_beg
    +#define ia64_spinlock_contention_end ia64_spinlock_contention_pre3_4_end
    +#else
    +extern char ia64_spinlock_contention[], ia64_spinlock_contention_end[];
    +#endif
    +#endif
    +
    static int
    default_handler(struct task_struct *task, void *buf, pfm_ovfl_arg_t *arg, struct pt_regs *regs, unsigned long stamp)
    {
    @@ -164,6 +175,14 @@ default_handler(struct task_struct *task
    * where did the fault happen (includes slot number)
    */
    ent->ip = regs->cr_iip | ((regs->cr_ipsr >> 41) & 0x3);
    +#ifdef CONFIG_SMP
    + /* Fix up the ip for code in the spinlock contention path. */
    + if ((ent->ip >= (unsigned long)ia64_spinlock_contention) &&
    + (ent->ip < (unsigned long)ia64_spinlock_contention_end))
    + ent->ip = regs->b6;
    +#endif
    + if (in_lock_functions(ent->ip))
    + ent->ip = regs->r28;

    ent->tstamp = stamp;
    ent->cpu = smp_processor_id();

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