linux-kernel - Re: [PATCH v2 2/2] perf tool: Fix ppid for synthesized fork events

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Date:	Mon, 30 Mar 2015 13:53:04 -0600
From:	David Ahern <dsahern@...il.com>
To:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
CC:	linux-kernel@...r.kernel.org, Don Zickus <dzickus@...hat.com>,
	Joe Mario <jmario@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 2/2] perf tool: Fix ppid for synthesized fork events

On 3/30/15 1:40 PM, Arnaldo Carvalho de Melo wrote:
>> @@ -81,6 +84,7 @@ static pid_t perf_event__get_comm_tgid(pid_t pid, char *comm, size_t len)
>>
>>   	name = strstr(bf, "Name:");
>>   	tgids = strstr(bf, "Tgid:");
>> +	ppids = strstr(bf, "PPid:");
>
> can't we make this:
>
> 	ppids = strstr(tgids, "PPid:");
>
> To speed it up a teeny little bit? 8-)

Sure, I thought about that as well, but it puts an assumption on order 
of the data in the file. Why have the assumption?

>
>>   	if (name) {
>>   		name += 5;  /* strlen("Name:") */
>> @@ -109,32 +113,51 @@ static pid_t perf_event__get_comm_tgid(pid_t pid, char *comm, size_t len)
>>   		if (nl)
>>   			*nl = '\0';
>>
>> -		tgid = atoi(tgids);
>> +		*tgid = atoi(tgids);
>>
>>   	} else
>>   		pr_debug("Tgid: string not found for pid %d\n", pid);
>>
>> -	return tgid;
>> +	if (ppids) {
>> +		ppids += 5;  /* strlen("PPid:") */
>> +
>> +		while (*ppids && isspace(*ppids))
>> +			++ppids;
>
> The above could be simplified to:
>
> 		while (isspace(*ppids))
> 			++ppids;

sure.

>
> $ cat isspace.c
> #include <ctype.h>
> #include <stdio.h>
> int main(void) { return printf("isspace('\\0')=%d\n", isspace('\0')); }
> $ ./isspace
> isspace('\0')=0
> $
>
>> +		nl = strchr(ppids, '\n');
>> +		if (nl)
>> +			 *nl = '\0';
>
> We also don't need to find and zero this '\n', as:
>
> $ cat atoi.c
> #include <string.h>
> #include <stdio.h>
> int main(void) { return printf("atoi(\"1234\\n\")=%d\n",
> atoi("1234\n")); }
> $ ./atoi
> atoi("1234\n")=1234
> $

ok. another assumption on implementation. fine with taking it out.

>
> <SNIP>
>
>> +	if (machine__is_host(machine)) {
>> +		if (perf_event__get_comm_ids(pid, event->comm.comm,
>> +					     sizeof(event->comm.comm),
>> +					     tgid, ppid) != 0) {
>> +			return -1;
>> +		}
>> +	} else
>> +		*tgid = machine->pid;
>
> Somebody, I think PeterZ and also Ingo, routinely asks for having {} on
> the else part of an if that has {}, please do so.

ack

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