[PATCH] ARCH_HAS_IRQ_PER_CPU avoids dead code in __do_IRQ()

[PATCH] ARCH_HAS_IRQ_PER_CPU avoids dead code in __do_IRQ()

[Karsten Wiese]

Hi Ingo,

from the bitkeeper logs I found you made the last
global-arch-relevant changes in this area.
Please comment or pass it on as appropriate.
Patch is for mainline 2.6.13-rc5.

    Thanks,
    Karsten 

From: Karsten Wiese <annabellesgarden@yahoo.de>

IRQ_PER_CPU is not used by all architectures.
To avoid dead code generation in __do_IRQ()
this patch introduces the macro ARCH_HAS_IRQ_PER_CPU.

ARCH_HAS_IRQ_PER_CPU is defined by architectures using
IRQ_PER_CPU in their
	include/asm_ARCH/irq.h
file.

Through grepping the tree I found the following
architectures currently use IRQ_PER_CPU:

	cris, ia64, ppc, ppc64 and parisc. 

Signed-off-by: Karsten Wiese <annabellesgarden@yahoo.de>



diff -upr linux-2.6.13_orig/include/asm-cris/irq.h linux-2.6.13/include/asm-cris/irq.h
--- linux-2.6.13_orig/include/asm-cris/irq.h	2005-08-06 16:44:41.000000000 +0200
+++ linux-2.6.13/include/asm-cris/irq.h	2005-08-06 18:06:48.000000000 +0200
@@ -1,6 +1,11 @@
 #ifndef _ASM_IRQ_H
 #define _ASM_IRQ_H
 
+/*
+ * IRQ line status macro IRQ_PER_CPU is used
+ */
+#define ARCH_HAS_IRQ_PER_CPU
+
 #include <asm/arch/irq.h>
 
 extern __inline__ int irq_canonicalize(int irq)
diff -upr linux-2.6.13_orig/include/asm-ia64/irq.h linux-2.6.13/include/asm-ia64/irq.h
--- linux-2.6.13_orig/include/asm-ia64/irq.h	2005-08-06 16:47:24.000000000 +0200
+++ linux-2.6.13/include/asm-ia64/irq.h	2005-08-06 18:06:53.000000000 +0200
@@ -14,6 +14,11 @@
 #define NR_IRQS		256
 #define NR_IRQ_VECTORS	NR_IRQS
 
+/*
+ * IRQ line status macro IRQ_PER_CPU is used
+ */
+#define ARCH_HAS_IRQ_PER_CPU
+
 static __inline__ int
 irq_canonicalize (int irq)
 {
diff -upr linux-2.6.13_orig/include/asm-parisc/irq.h linux-2.6.13/include/asm-parisc/irq.h
--- linux-2.6.13_orig/include/asm-parisc/irq.h	2005-08-06 16:50:29.000000000 +0200
+++ linux-2.6.13/include/asm-parisc/irq.h	2005-08-06 18:05:22.000000000 +0200
@@ -26,6 +26,11 @@
 
 #define NR_IRQS		(CPU_IRQ_MAX + 1)
 
+/*
+ * IRQ line status macro IRQ_PER_CPU is used
+ */
+#define ARCH_HAS_IRQ_PER_CPU
+
 static __inline__ int irq_canonicalize(int irq)
 {
 	return (irq == 2) ? 9 : irq;
diff -upr linux-2.6.13_orig/include/asm-ppc/irq.h linux-2.6.13/include/asm-ppc/irq.h
--- linux-2.6.13_orig/include/asm-ppc/irq.h	2005-08-02 13:55:51.000000000 +0200
+++ linux-2.6.13/include/asm-ppc/irq.h	2005-08-06 18:10:19.000000000 +0200
@@ -19,6 +19,11 @@
 #define IRQ_POLARITY_POSITIVE	0x2	/* high level or low->high edge */
 #define IRQ_POLARITY_NEGATIVE	0x0	/* low level or high->low edge */
 
+/*
+ * IRQ line status macro IRQ_PER_CPU is used
+ */
+#define ARCH_HAS_IRQ_PER_CPU
+
 #if defined(CONFIG_40x)
 #include <asm/ibm4xx.h>
 
diff -upr linux-2.6.13_orig/include/asm-ppc64/irq.h linux-2.6.13/include/asm-ppc64/irq.h
--- linux-2.6.13_orig/include/asm-ppc64/irq.h	2005-08-06 16:41:14.000000000 +0200
+++ linux-2.6.13/include/asm-ppc64/irq.h	2005-08-06 18:06:58.000000000 +0200
@@ -33,6 +33,11 @@
 #define IRQ_POLARITY_POSITIVE	0x2	/* high level or low->high edge */
 #define IRQ_POLARITY_NEGATIVE	0x0	/* low level or high->low edge */
 
+/*
+ * IRQ line status macro IRQ_PER_CPU is used
+ */
+#define ARCH_HAS_IRQ_PER_CPU
+
 #define get_irq_desc(irq) (&irq_desc[(irq)])
 
 /* Define a way to iterate across irqs. */
diff -upr linux-2.6.13_orig/include/linux/irq.h linux-2.6.13/include/linux/irq.h
--- linux-2.6.13_orig/include/linux/irq.h	2005-08-06 16:36:14.000000000 +0200
+++ linux-2.6.13/include/linux/irq.h	2005-08-06 16:36:30.000000000 +0200
@@ -32,7 +32,9 @@
 #define IRQ_WAITING	32	/* IRQ not yet seen - for autodetection */
 #define IRQ_LEVEL	64	/* IRQ level triggered */
 #define IRQ_MASKED	128	/* IRQ masked - shouldn't be seen again */
+#if defined(ARCH_HAS_IRQ_PER_CPU)
 #define IRQ_PER_CPU	256	/* IRQ is per CPU */
+#endif
 
 /*
  * Interrupt controller descriptor. This is all we need
diff -upr linux-2.6.13_orig/kernel/irq/handle.c linux-2.6.13/kernel/irq/handle.c
--- linux-2.6.13_orig/kernel/irq/handle.c	2005-08-06 15:53:37.000000000 +0200
+++ linux-2.6.13/kernel/irq/handle.c	2005-08-06 15:19:57.000000000 +0200
@@ -112,6 +112,7 @@ fastcall unsigned int __do_IRQ(unsigned 
 
 	kstat_this_cpu.irqs[irq]++;
 
+#if defined(ARCH_HAS_IRQ_PER_CPU)
 	if (desc->status & IRQ_PER_CPU) {
 		irqreturn_t action_ret;
 
@@ -123,6 +124,7 @@ fastcall unsigned int __do_IRQ(unsigned 
 		desc->handler->end(irq);
 		return 1;
 	}
+#endif
 
 	spin_lock(&desc->lock);
 	desc->handler->ack(irq);

	

	
		
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Re: [PATCH] ARCH_HAS_IRQ_PER_CPU avoids dead code in __do_IRQ()

[Ingo Oeser]

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Hi Karsten,

On Saturday 06 August 2005 18:14, Karsten Wiese wrote:
> From: Karsten Wiese <annabellesgarden@yahoo.de>
> 
> IRQ_PER_CPU is not used by all architectures.
> To avoid dead code generation in __do_IRQ()
> this patch introduces the macro ARCH_HAS_IRQ_PER_CPU.
> 
> ARCH_HAS_IRQ_PER_CPU is defined by architectures using
> IRQ_PER_CPU in their
> 	include/asm_ARCH/irq.h
> file.

Why not the other way around?

Just define IRQ_PER_CPU to 0 on architectures not needing it and
add a FAT comment there, that this disables it. Or make it a config option.

Then just leave the code as is and let GCC optimize the dead code
away without any changes in the C file. It works, I just checked it ;-)


Regards

Ingo Oeser


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Re: [PATCH] ARCH_HAS_IRQ_PER_CPU avoids dead code in __do_IRQ()

[Karsten Wiese]

Am Samstag, 6. August 2005 23:28 schrieb Ingo Oeser:
> Hi Karsten,
> 
> On Saturday 06 August 2005 18:14, Karsten Wiese wrote:
> > From: Karsten Wiese <annabellesgarden@yahoo.de>
> > 
> > IRQ_PER_CPU is not used by all architectures.
> > To avoid dead code generation in __do_IRQ()
> > this patch introduces the macro ARCH_HAS_IRQ_PER_CPU.
> > 
> > ARCH_HAS_IRQ_PER_CPU is defined by architectures using
> > IRQ_PER_CPU in their
> > 	include/asm_ARCH/irq.h
> > file.
> 
> Why not the other way around?
> 
> Just define IRQ_PER_CPU to 0 on architectures not needing it and
> add a FAT comment there, that this disables it. Or make it a config option.
> 
> Then just leave the code as is and let GCC optimize the dead code
> away without any changes in the C file. It works, I just checked it ;-)
> 
With my proposal the
	#if defined(ARCH_HAS_IRQ_PER_CPU)
	....
	#endif
lets readers of __do_IRQ() immediately grasp:
 "this block might not be compiled / depends an ARCH"
And you'll get compile error's using IRQ_PER_CPU on ie i386,
letting you immediately know,
that you've got to change something to be able to use IRQ_PER_CPU.

That are advantages I think.
Otherwise your proposal is ok for me too.

   Regards,
   Karsten

	

	
		
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Re: [PATCH] ARCH_HAS_IRQ_PER_CPU avoids dead code in __do_IRQ()

[Ingo Oeser]

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Hi Karsten,

On Sunday 07 August 2005 12:25, Karsten Wiese wrote:
> With my proposal the
> 	#if defined(ARCH_HAS_IRQ_PER_CPU)
> 	....
> 	#endif
> lets readers of __do_IRQ() immediately grasp:
>  "this block might not be compiled / depends an ARCH"
> And you'll get compile error's using IRQ_PER_CPU on ie i386,
> letting you immediately know,
> that you've got to change something to be able to use IRQ_PER_CPU.
> 
> That are advantages I think.

That's a valid argument. But an if is an if for the reader.
It is a conditional he has to be aware of and it usally has
no idention, if it is just inside "#if" instead of "if ()".

I have seen people seen missing "#if 0" [1] around code while 
reading it. Missing an normal if () is harder with proper idention.

A normal conditional has also the advantage, that the compiler
checks the code for syntactic and some semantic errors within it.

In an "#if 0" you can basically write any plain text[2] and any error
will go undetected, until it becomes an "#if 1".

Since your define is true for most compilations out there,
this argument is not very strong.

Last argument: Many kernel developers -- including Linus -- 
don't like "#if" in C files and prefer them in headers. 
Their reasons might be similiar to my own.


Regards

Ingo Oeser

[1] Let's just consider the values of the pre-processor symbols here, ok?
[2] Pavel Machek used this already to combine Makefile and C file :-)


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Re: [PATCH] ARCH_HAS_IRQ_PER_CPU avoids dead code in __do_IRQ()

[Karsten Wiese]

Am Sonntag, 7. August 2005 13:07 schrieb Ingo Oeser:
> Last argument: Many kernel developers -- including Linus -- 
> don't like "#if" in C files and prefer them in headers. 
> Their reasons might be similiar to my own.

What about writing
	if(CHECK_IRQ_PER_CPU(desc->status)) {
		...
	}
in __do_IRQ(),
and
	#if defined(ARCH_HAS_IRQ_PER_CPU)
		#define IRQ_PER_CPU	256	/* IRQ is per CPU */
		#define CHECK_IRQ_PER_CPU(var) ((var) & IRQ_PER_CPU)
	#else
		#define CHECK_IRQ_PER_CPU(var) 0
	#endif
in "include/linux/irq.h" then?

   Gruesse,
   Karsten

	

	
		
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