linux-kernel - Re: [PATCH v2] tracing: shrink max latency ringbuffer if unnecessary

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Message-ID: <4C2C5F44.7010006@cn.fujitsu.com>
Date:	Thu, 01 Jul 2010 17:26:28 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
CC:	rostedt@...dmis.org, LKML <linux-kernel@...r.kernel.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH v2] tracing: shrink max latency ringbuffer if unnecessary

KOSAKI Motohiro wrote:
> 
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> ---
>  kernel/trace/trace.c              |   39 ++++++++++++++++++++++++++++++------
>  kernel/trace/trace.h              |    1 +
>  kernel/trace/trace_irqsoff.c      |    3 ++
>  kernel/trace/trace_sched_wakeup.c |    2 +
>  4 files changed, 38 insertions(+), 7 deletions(-)
> 

Reviewed-by: Lai Jiangshan <laijs@...fujitsu.com


> -
> +	if (current_trace && current_trace->use_max_tr) {
> +		/*
> +		 * We don't free the ring buffer. instead, resize it because
> +		 * The max_tr ring buffer has some state (e.g. ring->clock) and
> +		 * we want preserve it.
> +		 */
> +		ring_buffer_resize(max_tr.buffer, 1);
> +		max_tr.entries = 1;
> +	}
>  	destroy_trace_option_files(topts);
>  
>  	current_trace = t;
>  
>  	topts = create_trace_option_files(current_trace);

I think we can skip the two resize when current_trace->use_max_tr==1 && t->use_max_tr==1

> +	if (current_trace->use_max_tr) {
> +		ret = ring_buffer_resize(max_tr.buffer, global_trace.entries);
> +		if (ret < 0)
> +			goto out;
> +		max_tr.entries = global_trace.entries;
> +	}
>  
>  	if (t->init) {
>  		ret = tracer_init(t, tr);

Does we need to shrink it when tracer_init() fails?
Although tracer_init() hardly fails, and there is no bad effect even we don't shrink it.
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