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trace: use this_cpu_ptr per-cpu helper

PATCH Superseded Shan Wei 2 participants 3 messages Nov 9, 2012 – Nov 12, 2012

Subsystems (2)
Block layer Tracing

v3 of 4 Superseded Latest is v4 →

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Shan Wei

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#0 lore raw

PATCH v3 7/9 trace: use this_cpu_ptr per-cpu helper

From: Shan Wei <[email protected]>

Signed-off-by Shan Wei <[email protected]>

---
v3:
directly return member address of per-cpu variable.

---
 kernel/trace/blktrace.c |    2 +-
 kernel/trace/trace.c    |    5 +----
 2 files changed, 2 insertions(+), 5 deletions(-)
kernel/trace/blktrace.c +1 -1
index c0bd030..71259e2 100644
@@ -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);
kernel/trace/trace.c +1 -4
index 31e4f55..65cb003 100644
@@ -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 (char *)this_cpu_ptr(&percpu_buffer->buffer);
 }
 
 static int alloc_percpu_trace_buffer(void)
Signature · 1 line
1.7.1
#1 lore raw

kernel/trace/trace.c static char *get_trace_buf(void) · line 1516

Quoted 3 lines · Shan Wei
kernel/trace/trace.c +1 -1
-	return buffer->buffer;
+	return (char *)this_cpu_ptr(&percpu_buffer->buffer);
 }

Add a comment to explain the cast?

author
#2 lore raw

Christoph Lameter said, at 2012/11/10 4:15:

Quoted 7 lines · Shan Wei

kernel/trace/trace.c static char *get_trace_buf(void) · line 1516

Quoted 4 lines
kernel/trace/trace.c +1 -1
-	return buffer->buffer;
+	return (char *)this_cpu_ptr(&percpu_buffer->buffer);
 }

Add a comment to explain the cast?

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 this cast.

I will submit v4 version patch which improve it.

Thanks~