linux-kernel - Re: [PATCH 3/3] relay: Add buffer-only channels; useful for early logging.

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Date:	Fri, 13 Jun 2008 10:04:57 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
CC:	tzanussi@...il.com, akpm@...ux-foundation.org,
	compudj@...stal.dyndns.org, linux-kernel@...r.kernel.org,
	righi.andrea@...il.com
Subject: Re: [PATCH 3/3] relay: Add buffer-only channels; useful for early
 logging.

Hi Eduard,

Eduard - Gabriel Munteanu wrote:
> @@ -578,12 +592,15 @@ struct rchan *relay_open(const char *base_filename,
>  	chan->alloc_size = FIX_SIZE(subbuf_size * n_subbufs);
>  	chan->parent = parent;
>  	chan->private_data = private_data;
> -	strlcpy(chan->base_filename, base_filename, NAME_MAX);
> +	if (base_filename) {
> +		chan->has_base_filename = 1;
> +		strlcpy(chan->base_filename, base_filename, NAME_MAX);
> +	}
>  	setup_callbacks(chan, cb);
>  	kref_init(&chan->kref);
>  
>  	mutex_lock(&relay_channels_mutex);
> -	for_each_online_cpu(i) {
> +	for_each_present_cpu(i) {
>  		chan->buf[i] = relay_open_buf(chan, i);
>  		if (!chan->buf[i])
>  			goto free_bufs;
> @@ -594,7 +611,7 @@ struct rchan *relay_open(const char *base_filename,
>  	return chan;
>  
>  free_bufs:
> -	for_each_online_cpu(i) {
> +	for_each_present_cpu(i) {
>  		if (!chan->buf[i])
>  			break;
>  		relay_close_buf(chan->buf[i]);

Why do we need to change for_each_online_cpu to for_each_present_cpu?
I guess it's because we don't have all the CPUs online at early
boot? Wouldn't it then be better to implement CPU hotplug support
instead?

		Pekka
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