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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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