linux-kernel - Re: [PATCH] tracing: Optimize event type allocation with IDA

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Message-Id: <20221109222650.ce6c22e231345f6852f6956f@kernel.org>
Date:   Wed, 9 Nov 2022 22:26:50 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     Zheng Yejian <zhengyejian1@...wei.com>
Cc:     <rostedt@...dmis.org>, <linux-kernel@...r.kernel.org>,
        <bpf@...r.kernel.org>
Subject: Re: [PATCH] tracing: Optimize event type allocation with IDA

On Wed, 9 Nov 2022 11:23:52 +0800
Zheng Yejian <zhengyejian1@...wei.com> wrote:

> After commit 060fa5c83e67 ("tracing/events: reuse trace event ids after
>  overflow"), trace events with dynamic type are linked up in list
> 'ftrace_event_list' through field 'trace_event.list'. Then when max
> event type number used up, it's possible to reuse type number of some
> freed one by traversing 'ftrace_event_list'.
> 
> As instead, using IDA to manage available type numbers can make codes
> simpler and then the field 'trace_event.list' can be dropped.
> 
> Since 'struct trace_event' is used in static tracepoints, drop
> 'trace_event.list' can make vmlinux smaller. Local test with about 2000
> tracepoints, vmlinux reduced about 64KB:
>   before：-rwxrwxr-x 1 root root 76669448 Nov  8 17:14 vmlinux
>   after： -rwxrwxr-x 1 root root 76604176 Nov  8 17:15 vmlinux
> 

This looks good to me, I just have one comment below.

> Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
> ---
>  include/linux/trace_events.h |  1 -
>  kernel/trace/trace_output.c  | 65 +++++++++---------------------------
>  2 files changed, 15 insertions(+), 51 deletions(-)
> 
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index 20749bd9db71..bb2053246d6a 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -136,7 +136,6 @@ struct trace_event_functions {
>  
>  struct trace_event {
>  	struct hlist_node		node;
> -	struct list_head		list;
>  	int				type;
>  	struct trace_event_functions	*funcs;
>  };
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index 67f47ea27921..314d175dee3a 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c

Please include linux/idr.h in this source file explicitly beause
IDA APIs are defined in it.

Thank you,

> @@ -21,8 +21,6 @@ DECLARE_RWSEM(trace_event_sem);
>  
>  static struct hlist_head event_hash[EVENT_HASHSIZE] __read_mostly;
>  
> -static int next_event_type = __TRACE_LAST_TYPE;
> -
>  enum print_line_t trace_print_bputs_msg_only(struct trace_iterator *iter)
>  {
>  	struct trace_seq *s = &iter->seq;
> @@ -688,38 +686,23 @@ struct trace_event *ftrace_find_event(int type)
>  	return NULL;
>  }
>  
> -static LIST_HEAD(ftrace_event_list);
> +static DEFINE_IDA(trace_event_ida);
>  
> -static int trace_search_list(struct list_head **list)
> +static void free_trace_event_type(int type)
>  {
> -	struct trace_event *e = NULL, *iter;
> -	int next = __TRACE_LAST_TYPE;
> -
> -	if (list_empty(&ftrace_event_list)) {
> -		*list = &ftrace_event_list;
> -		return next;
> -	}
> +	if (type >= __TRACE_LAST_TYPE)
> +		ida_free(&trace_event_ida, type);
> +}
>  
> -	/*
> -	 * We used up all possible max events,
> -	 * lets see if somebody freed one.
> -	 */
> -	list_for_each_entry(iter, &ftrace_event_list, list) {
> -		if (iter->type != next) {
> -			e = iter;
> -			break;
> -		}
> -		next++;
> -	}
> +static int alloc_trace_event_type(void)
> +{
> +	int next;
>  
> -	/* Did we used up all 65 thousand events??? */
> -	if (next > TRACE_EVENT_TYPE_MAX)
> +	/* Skip static defined type numbers */
> +	next = ida_alloc_range(&trace_event_ida, __TRACE_LAST_TYPE,
> +			       TRACE_EVENT_TYPE_MAX, GFP_KERNEL);
> +	if (next < 0)
>  		return 0;
> -
> -	if (e)
> -		*list = &e->list;
> -	else
> -		*list = &ftrace_event_list;
>  	return next;
>  }
>  
> @@ -761,28 +744,10 @@ int register_trace_event(struct trace_event *event)
>  	if (WARN_ON(!event->funcs))
>  		goto out;
>  
> -	INIT_LIST_HEAD(&event->list);
> -
>  	if (!event->type) {
> -		struct list_head *list = NULL;
> -
> -		if (next_event_type > TRACE_EVENT_TYPE_MAX) {
> -
> -			event->type = trace_search_list(&list);
> -			if (!event->type)
> -				goto out;
> -
> -		} else {
> -
> -			event->type = next_event_type++;
> -			list = &ftrace_event_list;
> -		}
> -
> -		if (WARN_ON(ftrace_find_event(event->type)))
> +		event->type = alloc_trace_event_type();
> +		if (!event->type)
>  			goto out;
> -
> -		list_add_tail(&event->list, list);
> -
>  	} else if (WARN(event->type > __TRACE_LAST_TYPE,
>  			"Need to add type to trace.h")) {
>  		goto out;
> @@ -819,7 +784,7 @@ EXPORT_SYMBOL_GPL(register_trace_event);
>  int __unregister_trace_event(struct trace_event *event)
>  {
>  	hlist_del(&event->node);
> -	list_del(&event->list);
> +	free_trace_event_type(event->type);
>  	return 0;
>  }
>  
> -- 
> 2.25.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>