Re: hot cache line due to note_interrupt()

From: Jack Steiner
Date: Fri Nov 14 2003 - 12:48:33 EST

On Tue, Nov 11, 2003 at 11:58:04AM -0800, Andrew Morton wrote:
> Ravikiran G Thirumalai <kiran@xxxxxxxxxx> wrote:
> >
> > On Mon, Nov 10, 2003 at 03:58:44PM -0600, Jack Steiner wrote:
> > >
> > > I dont know the background on note_interrupt() in arch/ia64/kernel/irq.c,
> > > but I had to disable the function on our large systems (IA64).
> > >
> > > The function updates a counter in the irq_desc_t table. An entry in this table
> > > is shared by all cpus that take a specific interrupt #. For most interrupt #'s,
> > > this is a problem but it is prohibitive for the timer tick on big systems.
> > >
> > > Updating the counter causes a cache line to be bounced between
> > > cpus at a rate of at least HZ*active_cpus. (The number of bus transactions
> >
> > The answer to this is probably alloc_percpu for the counters.
>
> Or just make noirqdebug the default.
>
> The note_interrupt() stuff is only useful for diagnosing mysterious lockups
> (and hasn't proven useful for that, actually). It should be disabled for
> production use.
>


Probably too late for 2.6.0, but here is a patch that disables noirqdebug:



# This is a BitKeeper generated patch for the following project:
# Project Name: Linux kernel tree
# This patch format is intended for GNU patch command version 2.5 or higher.
# This patch includes the following deltas:
# ChangeSet 1.1438 -> 1.1439
# arch/i386/kernel/irq.c 1.45 -> 1.46
# arch/mips/kernel/irq.c 1.14 -> 1.15
# arch/ppc64/kernel/irq.c 1.36 -> 1.37
# arch/ia64/kernel/irq.c 1.31 -> 1.32
#
# The following is the BitKeeper ChangeSet Log
# --------------------------------------------
# 03/11/14 steiner@xxxxxxxxxxxxxxxxxxxxxxx 1.1439
# Change the default value for "irqdebug" so that it is disabled.
# Rename option from "noirqdebug" to "irqdebug".
# --------------------------------------------
#
diff -Nru a/arch/i386/kernel/irq.c b/arch/i386/kernel/irq.c
--- a/arch/i386/kernel/irq.c Fri Nov 14 11:18:07 2003
+++ b/arch/i386/kernel/irq.c Fri Nov 14 11:18:07 2003
@@ -259,16 +259,16 @@
}
}

-static int noirqdebug;
+static int irqdebug;

-static int __init noirqdebug_setup(char *str)
+static int __init irqdebug_setup(char *str)
{
- noirqdebug = 1;
- printk("IRQ lockup detection disabled\n");
+ irqdebug = 1;
+ printk("IRQ lockup detection enabled\n");
return 1;
}

-__setup("noirqdebug", noirqdebug_setup);
+__setup("irqdebug", irqdebug_setup);

/*
* If 99,900 of the previous 100,000 interrupts have not been handled then
@@ -484,7 +484,7 @@
spin_unlock(&desc->lock);
action_ret = handle_IRQ_event(irq, &regs, action);
spin_lock(&desc->lock);
- if (!noirqdebug)
+ if (irqdebug)
note_interrupt(irq, desc, action_ret);
if (likely(!(desc->status & IRQ_PENDING)))
break;
diff -Nru a/arch/ia64/kernel/irq.c b/arch/ia64/kernel/irq.c
--- a/arch/ia64/kernel/irq.c Fri Nov 14 11:18:07 2003
+++ b/arch/ia64/kernel/irq.c Fri Nov 14 11:18:07 2003
@@ -283,16 +283,16 @@
}
}

-static int noirqdebug;
+static int irqdebug;

-static int __init noirqdebug_setup(char *str)
+static int __init irqdebug_setup(char *str)
{
- noirqdebug = 1;
- printk("IRQ lockup detection disabled\n");
+ irqdebug = 1;
+ printk("IRQ lockup detection enabled\n");
return 1;
}

-__setup("noirqdebug", noirqdebug_setup);
+__setup("irqdebug", irqdebug_setup);

/*
* If 99,900 of the previous 100,000 interrupts have not been handled then
@@ -457,7 +457,7 @@
desc->handler->ack(irq);
action_ret = handle_IRQ_event(irq, regs, desc->action);
desc->handler->end(irq);
- if (!noirqdebug)
+ if (irqdebug)
note_interrupt(irq, desc, action_ret);
} else {
spin_lock(&desc->lock);
@@ -504,7 +504,7 @@
spin_unlock(&desc->lock);
action_ret = handle_IRQ_event(irq, regs, action);
spin_lock(&desc->lock);
- if (!noirqdebug)
+ if (irqdebug)
note_interrupt(irq, desc, action_ret);
if (!(desc->status & IRQ_PENDING))
break;
diff -Nru a/arch/mips/kernel/irq.c b/arch/mips/kernel/irq.c
--- a/arch/mips/kernel/irq.c Fri Nov 14 11:18:07 2003
+++ b/arch/mips/kernel/irq.c Fri Nov 14 11:18:07 2003
@@ -191,16 +191,16 @@
}
}

-static int noirqdebug;
+static int irqdebug;

-static int __init noirqdebug_setup(char *str)
+static int __init irqdebug_setup(char *str)
{
- noirqdebug = 1;
- printk("IRQ lockup detection disabled\n");
+ irqdebug = 1;
+ printk("IRQ lockup detection enabled\n");
return 1;
}

-__setup("noirqdebug", noirqdebug_setup);
+__setup("irqdebug", irqdebug_setup);

/*
* If 99,900 of the previous 100,000 interrupts have not been handled then
@@ -396,7 +396,7 @@
spin_unlock(&desc->lock);
action_ret = handle_IRQ_event(irq, regs, action);
spin_lock(&desc->lock);
- if (!noirqdebug)
+ if (irqdebug)
note_interrupt(irq, desc, action_ret);
if (likely(!(desc->status & IRQ_PENDING)))
break;
diff -Nru a/arch/ppc64/kernel/irq.c b/arch/ppc64/kernel/irq.c
--- a/arch/ppc64/kernel/irq.c Fri Nov 14 11:18:07 2003
+++ b/arch/ppc64/kernel/irq.c Fri Nov 14 11:18:07 2003
@@ -416,16 +416,16 @@
}
}

-static int noirqdebug;
+static int irqdebug;

-static int __init noirqdebug_setup(char *str)
+static int __init irqdebug_setup(char *str)
{
- noirqdebug = 1;
- printk("IRQ lockup detection disabled\n");
+ irqdebug = 1;
+ printk("IRQ lockup detection enabled\n");
return 1;
}

-__setup("noirqdebug", noirqdebug_setup);
+__setup("irqdebug", irqdebug_setup);

/*
* If 99,900 of the previous 100,000 interrupts have not been handled then
@@ -538,7 +538,7 @@
spin_unlock(&desc->lock);
action_ret = handle_irq_event(irq, regs, action);
spin_lock(&desc->lock);
- if (!noirqdebug)
+ if (irqdebug)
note_interrupt(irq, desc, action_ret);
if (likely(!(desc->status & IRQ_PENDING)))
break;

--
Thanks

Jack Steiner (steiner@xxxxxxx) 651-683-5302
Principal Engineer SGI - Silicon Graphics, Inc.


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