[Adeos-main] [PATCH] avoid suboptimal use of ipipe_lock_cpu

[Adeos-main] [PATCH] avoid suboptimal use of ipipe_lock_cpu

[Jan Kiszka]

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Hi,

while disassembling that bug in start_kernel, I noticed that
ipipe_lock_cpu(flags) is used in a suboptimal way in some
ipipe_XXX_head() services, i.e. when the flags are actually of no
interest. The compiler still generates the unneeded pushf/pop <reg>, and
this in a hot-path.

Attached patch should perform better. Lightly tested, but QEMU SMP still
works here.

Jan

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---
 include/linux/ipipe.h |    8 ++++----
 kernel/ipipe/core.c   |    8 ++++----
 2 files changed, 8 insertions(+), 8 deletions(-)

Index: linux-2.6.19/include/linux/ipipe.h
===================================================================
--- linux-2.6.19.orig/include/linux/ipipe.h
+++ linux-2.6.19/include/linux/ipipe.h
@@ -471,18 +471,18 @@ static inline void ipipe_restore_pipelin
 static inline void ipipe_stall_pipeline_head(void)
 {
 	ipipe_declare_cpuid;
-	unsigned long flags;
 
-	ipipe_lock_cpu(flags);
+	local_irq_disable_hw();
+	ipipe_load_cpuid();
 	__set_bit(IPIPE_STALL_FLAG, &__ipipe_pipeline_head()->cpudata[cpuid].status);
 }
 
 static inline unsigned long ipipe_test_and_stall_pipeline_head(void)
 {
-	unsigned long flags;
 	ipipe_declare_cpuid;
 
-	ipipe_lock_cpu(flags);
+	local_irq_disable_hw();
+	ipipe_load_cpuid();
 	return __test_and_set_bit(IPIPE_STALL_FLAG, &__ipipe_pipeline_head()->cpudata[cpuid].status);
 }
 
Index: linux-2.6.19/kernel/ipipe/core.c
===================================================================
--- linux-2.6.19.orig/kernel/ipipe/core.c
+++ linux-2.6.19/kernel/ipipe/core.c
@@ -303,10 +303,10 @@ void fastcall ipipe_restore_pipeline_fro
 void ipipe_unstall_pipeline_head(void)
 {
 	struct ipipe_domain *head;
-	unsigned long flags;
 	ipipe_declare_cpuid;
 
-	ipipe_lock_cpu(flags);
+	local_irq_disable_hw();
+	ipipe_load_cpuid();
 	head = __ipipe_pipeline_head();
 	__clear_bit(IPIPE_STALL_FLAG, &head->cpudata[cpuid].status);
 
@@ -323,9 +323,9 @@ void ipipe_unstall_pipeline_head(void)
 void fastcall __ipipe_restore_pipeline_head(struct ipipe_domain *head, unsigned long x)
 {
 	ipipe_declare_cpuid;
-	unsigned long flags;
 
-	ipipe_lock_cpu(flags);
+	local_irq_disable_hw();
+	ipipe_load_cpuid();
 
 	if (x) {
 #ifdef CONFIG_DEBUG_KERNEL

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Re: [Adeos-main] [PATCH] avoid suboptimal use of ipipe_lock_cpu

[Philippe Gerum]

On Wed, 2006-12-13 at 18:58 +0100, Jan Kiszka wrote:
> Hi,
> 
> while disassembling that bug in start_kernel, I noticed that
> ipipe_lock_cpu(flags) is used in a suboptimal way in some
> ipipe_XXX_head() services, i.e. when the flags are actually of no
> interest. The compiler still generates the unneeded pushf/pop <reg>, and
> this in a hot-path.
> 
> Attached patch should perform better. Lightly tested, but QEMU SMP still
> works here.

Merged, thanks.

> 
> Jan
> plain text document attachment (avoid-ipipe_lock_cpu.patch)
> ---
>  include/linux/ipipe.h |    8 ++++----
>  kernel/ipipe/core.c   |    8 ++++----
>  2 files changed, 8 insertions(+), 8 deletions(-)
> 
> Index: linux-2.6.19/include/linux/ipipe.h
> ===================================================================
> --- linux-2.6.19.orig/include/linux/ipipe.h
> +++ linux-2.6.19/include/linux/ipipe.h
> @@ -471,18 +471,18 @@ static inline void ipipe_restore_pipelin
>  static inline void ipipe_stall_pipeline_head(void)
>  {
>  	ipipe_declare_cpuid;
> -	unsigned long flags;
>  
> -	ipipe_lock_cpu(flags);
> +	local_irq_disable_hw();
> +	ipipe_load_cpuid();
>  	__set_bit(IPIPE_STALL_FLAG, &__ipipe_pipeline_head()->cpudata[cpuid].status);
>  }
>  
>  static inline unsigned long ipipe_test_and_stall_pipeline_head(void)
>  {
> -	unsigned long flags;
>  	ipipe_declare_cpuid;
>  
> -	ipipe_lock_cpu(flags);
> +	local_irq_disable_hw();
> +	ipipe_load_cpuid();
>  	return __test_and_set_bit(IPIPE_STALL_FLAG, &__ipipe_pipeline_head()->cpudata[cpuid].status);
>  }
>  
> Index: linux-2.6.19/kernel/ipipe/core.c
> ===================================================================
> --- linux-2.6.19.orig/kernel/ipipe/core.c
> +++ linux-2.6.19/kernel/ipipe/core.c
> @@ -303,10 +303,10 @@ void fastcall ipipe_restore_pipeline_fro
>  void ipipe_unstall_pipeline_head(void)
>  {
>  	struct ipipe_domain *head;
> -	unsigned long flags;
>  	ipipe_declare_cpuid;
>  
> -	ipipe_lock_cpu(flags);
> +	local_irq_disable_hw();
> +	ipipe_load_cpuid();
>  	head = __ipipe_pipeline_head();
>  	__clear_bit(IPIPE_STALL_FLAG, &head->cpudata[cpuid].status);
>  
> @@ -323,9 +323,9 @@ void ipipe_unstall_pipeline_head(void)
>  void fastcall __ipipe_restore_pipeline_head(struct ipipe_domain *head, unsigned long x)
>  {
>  	ipipe_declare_cpuid;
> -	unsigned long flags;
>  
> -	ipipe_lock_cpu(flags);
> +	local_irq_disable_hw();
> +	ipipe_load_cpuid();
>  
>  	if (x) {
>  #ifdef CONFIG_DEBUG_KERNEL
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-- 
Philippe.