[PATCH v4 7/9] trace: use this_cpu_ptr per-cpu helper

[PATCH v4 7/9] trace: use this_cpu_ptr per-cpu helper

[Shan Wei]

From: Shan Wei <davidshan@tencent.com>

typeof(&buffer) is a pointer to array of 1024 char, or char (*)[1024].
But, typeof(&buffer[0]) is a pointer to char which match the return type of get_trace_buf().
As well-known, the value of &buffer is equal to &buffer[0].
so return this_cpu_ptr(&percpu_buffer->buffer[0]) can avoid type cast. 

Signed-off-by: Shan Wei <davidshan@tencent.com>
---
v4: avoid type cast using &percpu_buffer->buffer[0].
---
 kernel/trace/blktrace.c |    2 +-
 kernel/trace/trace.c    |    5 +----
 2 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index c0bd030..71259e2 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -147,7 +147,7 @@ void __trace_note_message(struct blk_trace *bt, const char *fmt, ...)
 		return;
 
 	local_irq_save(flags);
-	buf = per_cpu_ptr(bt->msg_data, smp_processor_id());
+	buf = this_cpu_ptr(bt->msg_data);
 	va_start(args, fmt);
 	n = vscnprintf(buf, BLK_TN_MAX_MSG, fmt, args);
 	va_end(args);
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 31e4f55..65cb003 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1495,7 +1495,6 @@ static struct trace_buffer_struct *trace_percpu_nmi_buffer;
 static char *get_trace_buf(void)
 {
 	struct trace_buffer_struct *percpu_buffer;
-	struct trace_buffer_struct *buffer;
 
 	/*
 	 * If we have allocated per cpu buffers, then we do not
@@ -1513,9 +1512,7 @@ static char *get_trace_buf(void)
 	if (!percpu_buffer)
 		return NULL;
 
-	buffer = per_cpu_ptr(percpu_buffer, smp_processor_id());
-
-	return buffer->buffer;
+	return this_cpu_ptr(&percpu_buffer->buffer[0]);
 }
 
 static int alloc_percpu_trace_buffer(void)
-- 
1.7.1

Re: [PATCH v4 7/9] trace: use this_cpu_ptr per-cpu helper

[Shan Wei]

Shan Wei said, at 2012/11/13 9:53:
> From: Shan Wei <davidshan@tencent.com>
> 
> typeof(&buffer) is a pointer to array of 1024 char, or char (*)[1024].
> But, typeof(&buffer[0]) is a pointer to char which match the return type of get_trace_buf().
> As well-known, the value of &buffer is equal to &buffer[0].
> so return this_cpu_ptr(&percpu_buffer->buffer[0]) can avoid type cast. 
> 
> Signed-off-by: Shan Wei <davidshan@tencent.com>

Steven Rostedt,  would you like to pick it up to your tree?

> ---
> v4: avoid type cast using &percpu_buffer->buffer[0].
> ---
>  kernel/trace/blktrace.c |    2 +-
>  kernel/trace/trace.c    |    5 +----
>  2 files changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index c0bd030..71259e2 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -147,7 +147,7 @@ void __trace_note_message(struct blk_trace *bt, const char *fmt, ...)
>  		return;
>  
>  	local_irq_save(flags);
> -	buf = per_cpu_ptr(bt->msg_data, smp_processor_id());
> +	buf = this_cpu_ptr(bt->msg_data);
>  	va_start(args, fmt);
>  	n = vscnprintf(buf, BLK_TN_MAX_MSG, fmt, args);
>  	va_end(args);
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 31e4f55..65cb003 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -1495,7 +1495,6 @@ static struct trace_buffer_struct *trace_percpu_nmi_buffer;
>  static char *get_trace_buf(void)
>  {
>  	struct trace_buffer_struct *percpu_buffer;
> -	struct trace_buffer_struct *buffer;
>  
>  	/*
>  	 * If we have allocated per cpu buffers, then we do not
> @@ -1513,9 +1512,7 @@ static char *get_trace_buf(void)
>  	if (!percpu_buffer)
>  		return NULL;
>  
> -	buffer = per_cpu_ptr(percpu_buffer, smp_processor_id());
> -
> -	return buffer->buffer;
> +	return this_cpu_ptr(&percpu_buffer->buffer[0]);
>  }
>  
>  static int alloc_percpu_trace_buffer(void)
> 

Re: [PATCH v4 7/9] trace: use this_cpu_ptr per-cpu helper

[Shan Wei]

Shan Wei said, at 2012/11/16 16:34:
> Shan Wei said, at 2012/11/13 9:53:
>> From: Shan Wei <davidshan@tencent.com>
>>
>> typeof(&buffer) is a pointer to array of 1024 char, or char (*)[1024].
>> But, typeof(&buffer[0]) is a pointer to char which match the return type of get_trace_buf().
>> As well-known, the value of &buffer is equal to &buffer[0].
>> so return this_cpu_ptr(&percpu_buffer->buffer[0]) can avoid type cast. 
>>
>> Signed-off-by: Shan Wei <davidshan@tencent.com>
> 
> Steven Rostedt,  would you like to pick it up to your tree?

ping......................

Re: [PATCH v4 7/9] trace: use this_cpu_ptr per-cpu helper

[Steven Rostedt]

On Fri, 2012-11-30 at 14:38 +0800, Shan Wei wrote:
> Shan Wei said, at 2012/11/16 16:34:
> > Shan Wei said, at 2012/11/13 9:53:
> >> From: Shan Wei <davidshan@tencent.com>
> >>
> >> typeof(&buffer) is a pointer to array of 1024 char, or char (*)[1024].
> >> But, typeof(&buffer[0]) is a pointer to char which match the return type of get_trace_buf().
> >> As well-known, the value of &buffer is equal to &buffer[0].
> >> so return this_cpu_ptr(&percpu_buffer->buffer[0]) can avoid type cast. 
> >>
> >> Signed-off-by: Shan Wei <davidshan@tencent.com>
> > 
> > Steven Rostedt,  would you like to pick it up to your tree?
> 
> ping......................

Sorry for the late reply. I've been hacking on other things and my queue
of stuff for tip still hasn't been pulled yet. I'll pull this into my
tree, and see if I can get it in by the merge window. If the merge
window opens this weekend, I'll add this to my 3.9 queue.

-- Steve

[tip:perf/core] tracing: Use this_cpu_ptr per-cpu helper

[tip-bot for Shan Wei]

Commit-ID:  d8a0349c0cea477322c66ea9362f10c62fad5f62
Gitweb:     http://git.kernel.org/tip/d8a0349c0cea477322c66ea9362f10c62fad5f62
Author:     Shan Wei <davidshan@tencent.com>
AuthorDate: Tue, 13 Nov 2012 09:53:04 +0800
Committer:  Steven Rostedt <rostedt@goodmis.org>
CommitDate: Mon, 21 Jan 2013 13:22:30 -0500

tracing: Use this_cpu_ptr per-cpu helper

typeof(&buffer) is a pointer to array of 1024 char, or char (*)[1024].
But, typeof(&buffer[0]) is a pointer to char which match the return type of get_trace_buf().
As well-known, the value of &buffer is equal to &buffer[0].
so return this_cpu_ptr(&percpu_buffer->buffer[0]) can avoid type cast.

Link: http://lkml.kernel.org/r/50A1A800.3020102@gmail.com

Reviewed-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Shan Wei <davidshan@tencent.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/blktrace.c | 2 +-
 kernel/trace/trace.c    | 5 +----
 2 files changed, 2 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index c0bd030..71259e2 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -147,7 +147,7 @@ void __trace_note_message(struct blk_trace *bt, const char *fmt, ...)
 		return;
 
 	local_irq_save(flags);
-	buf = per_cpu_ptr(bt->msg_data, smp_processor_id());
+	buf = this_cpu_ptr(bt->msg_data);
 	va_start(args, fmt);
 	n = vscnprintf(buf, BLK_TN_MAX_MSG, fmt, args);
 	va_end(args);
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 3c13e46..f8b7c62 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1517,7 +1517,6 @@ static struct trace_buffer_struct *trace_percpu_nmi_buffer;
 static char *get_trace_buf(void)
 {
 	struct trace_buffer_struct *percpu_buffer;
-	struct trace_buffer_struct *buffer;
 
 	/*
 	 * If we have allocated per cpu buffers, then we do not
@@ -1535,9 +1534,7 @@ static char *get_trace_buf(void)
 	if (!percpu_buffer)
 		return NULL;
 
-	buffer = per_cpu_ptr(percpu_buffer, smp_processor_id());
-
-	return buffer->buffer;
+	return this_cpu_ptr(&percpu_buffer->buffer[0]);
 }
 
 static int alloc_percpu_trace_buffer(void)