Re: [PATCH v3 1/2] trace-cmd: Optimize how pid filters are expressed

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 16 Apr 2019 02:00:15 +0300
Slavomir Kaslev <kaslevs@vmware.com> wrote:

>  static char *make_pid_filter(char *curr_filter, const char *field)
>  {
> +	int curr_len = 0, last_exclude = -1;

Small nit. Usually when adding multiple variables on one line like
this, the variables should be related. Because curr_len and
last_exclude are not related, it is best to keep them separate.

> +	int start_pid = -1, last_pid = -1;

start_pid and last_pid are fine on the same line or separate.

> +	char *filter = NULL, *save;


Note, It's better to keep variables separate. It makes it easier to see
them and also when code changes and you get the "variable x is not
used" warnings from gcc, it's easier to remove them. In emacs it brings
you to the warning and places the cursor on the problem line. Then a
simple "delete line" works well.

save could also be moved below.

>  	struct filter_pids *p;
> -	char *filter;
> -	char *orit;
> -	char *match;
> -	char *str;
> -	int curr_len = 0;
> -	int len;
>  
>  	/* Use the new method if possible */
>  	if (have_set_event_pid)
>  		return NULL;
>  
> -	len = len_filter_pids + (strlen(field) + strlen("(==)||")) * nr_filter_pids;
> -
> -	if (curr_filter) {
> -		curr_len = strlen(curr_filter);
> -		filter = realloc(curr_filter, curr_len + len + strlen("(&&())"));
> -		if (!filter)
> -			die("realloc");
> -		memmove(filter+1, curr_filter, curr_len);
> -		filter[0] = '(';
> -		strcat(filter, ")&&(");
> -		curr_len = strlen(filter);
> -	} else
> -		filter = malloc(len);
> -	if (!filter)
> -		die("Failed to allocate pid filter");
> -
> -	/* Last '||' that is not used will cover the \0 */
> -	str = filter + curr_len;
> +	if (!filter_pids)
> +		return curr_filter;
>  
>  	for (p = filter_pids; p; p = p->next) {
> -		if (p->exclude) {
> -			match = "!=";
> -			orit = "&&";
> -		} else {
> -			match = "==";
> -			orit = "||";
> +		/* PIDs are inserted in `filter_pids` from the front and that's

Comment notation should be:

		/*
		 * PIDs are inserted in ...

Only the Networking folks are allowed to do it that way in the
kernel ;-)

> +		 * why we expect them in descending order here.
> +		 */
> +		if (p->pid == last_pid - 1 && p->exclude == last_exclude) {
> +			last_pid = p->pid;
> +			continue;
>  		}
> -		if (p == filter_pids)
> -			orit = "";
>  
> -		len = sprintf(str, "%s(%s%s%d)", orit, field, match, p->pid);
> -		str += len;
> +		if (start_pid != -1)
> +			append_filter_pid_range(&filter, &curr_len, field,
> +						last_pid, start_pid,
> +						last_exclude);
> +
> +		start_pid = last_pid = p->pid;
> +		last_exclude = p->exclude;
> +
>  	}
> +	append_filter_pid_range(&filter, &curr_len, field,
> +				last_pid, start_pid, last_exclude);
>  
> -	if (curr_len)
> -		sprintf(str, ")");
> +	if (curr_filter) {

As save is only used here, we could have:

		char *save = filter;

> +		save = filter;
> +		asprintf(&filter, "(%s)&&(%s)", curr_filter, filter);
> +		free(save);
> +	}
>  
>  	return filter;
>  }

-- Steve