linux-kernel - Re: [PATCH v4 7/9] trace: use this_cpu

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Message-ID: <50A5FA84.8080106@gmail.com>
Date:	Fri, 16 Nov 2012 16:34:12 +0800
From:	Shan Wei <shanwei88@...il.com>
To:	rostedt@...dmis.org
CC:	Shan Wei <shanwei88@...il.com>, fweisbec@...il.com,
	Kernel-Maillist <linux-kernel@...r.kernel.org>, mingo@...hat.com,
	cl@...ux-foundation.org, Tejun Heo <htejun@...il.com>
Subject: Re: [PATCH v4 7/9] trace: use this_cpu_ptr per-cpu helper

Shan Wei said, at 2012/11/13 9:53:
> From: Shan Wei <davidshan@...cent.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@...cent.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)
> 

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