linux-kernel - Re: [PATCH 5/9] ftrace: use this_cpu

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Message-ID: <0000013ab7ebaffd-8b5d50e4-8ca9-4d40-a843-c343cbc70dbc-000000@email.amazonses.com>
Date:	Wed, 31 Oct 2012 17:43:27 +0000
From:	Christoph Lameter <cl@...ux.com>
To:	Shan Wei <shanwei88@...il.com>
cc:	rostedt@...dmis.org, fweisbec@...il.com, mingo@...hat.com,
	Kernel-Maillist <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/9] ftrace: use this_cpu_ptr per-cpu helper

On Wed, 31 Oct 2012, Shan Wei wrote:

> diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
> index a763888..7c9fde7 100644
> --- a/include/trace/ftrace.h
> +++ b/include/trace/ftrace.h
> @@ -638,7 +638,6 @@ __attribute__((section("_ftrace_events"))) *__event_##call = &event_##call
>   *	struct trace_entry *ent;
>   *	int __entry_size;
>   *	int __data_size;
> - *	int __cpu
>   *	int pc;
>   *
>   *	pc = preempt_count();
> @@ -654,7 +653,6 @@ __attribute__((section("_ftrace_events"))) *__event_##call = &event_##call
>   *	// Protect the non nmi buffer
>   *	// This also protects the rcu read side
>   *	local_irq_save(irq_flags);
> - *	__cpu = smp_processor_id();
>   *
>   *	if (in_nmi())
>   *		trace_buf = rcu_dereference_sched(perf_trace_buf_nmi);
> @@ -664,7 +662,7 @@ __attribute__((section("_ftrace_events"))) *__event_##call = &event_##call
>   *	if (!trace_buf)
>   *		goto end;
>   *
> - *	trace_buf = per_cpu_ptr(trace_buf, __cpu);
> + *	trace_buf = this_cpu_ptr(trace_buf);
>   *
>   * 	// Avoid recursion from perf that could mess up the buffer
>   * 	if (trace_buf->recursion++)

Reviewed-by: Christoph Lameter <cl@...ux.com>

Code could be further reduced by not doing the this_cpu_ptr op but using
this_cpu_read later instead.

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