linux-kernel - Re: [PATCH 3/3] perf script: dump software events and samples from hardware-based profiling

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Date:	Thu, 3 Mar 2011 04:05:19 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	David Ahern <daahern@...co.com>
Cc:	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	acme@...stprotocols.net, mingo@...e.hu, peterz@...radead.org,
	paulus@...ba.org, tglx@...utronix.de
Subject: Re: [PATCH 3/3] perf script: dump software events and samples from
 hardware-based profiling

On Wed, Mar 02, 2011 at 10:29:20AM -0700, David Ahern wrote:
> @@ -763,6 +783,18 @@ int cmd_script(int argc, const char **argv, const char *prefix __used)
>  		exit(-1);
>  	}
>  
> +	if (no_callchain)
> +		symbol_conf.use_callchain = false;
> +
> +	else {
> +		symbol_conf.use_callchain = true;
> +		if (callchain_register_param(&callchain_param) < 0) {

That call doesn't seem needed. Register callchain params is only useful
for later callchain sorting.

> +			error("Can't register callchain params\n");
> +			err = -EINVAL;
> +			goto out;
> +		}
> +	}
> +
>  	if (rec_script_path)
>  		script_path = rec_script_path;
>  	if (rep_script_path)
[...]
> +void perf_session__print_sample(union perf_event *event,
> +				struct perf_sample *sample,
> +				struct perf_session *session,
> +				struct perf_event_attr *attr,
> +				bool show_unresolved)
> +{
> +	struct callchain_cursor_node *node, *prev;
> +	struct addr_location al;
> +	const char *evname = NULL;
> +	const char *comm;
> +	const char *symname, *dsoname;
> +	u32 cpu = -1;
> +	u64 secs = 0, usecs = 0;
> +
> +	if (perf_event__preprocess_sample(event, session, &al, sample,
> +					  NULL) < 0) {
> +		error("problem processing %d event, skipping it.\n",
> +			event->header.type);
> +		return;
> +	}
> +
> +	if (session->sample_type & PERF_SAMPLE_TIME) {
> +		u64 nsecs = sample->time;
> +		secs = nsecs / NSECS_PER_SEC;
> +		nsecs -= secs * NSECS_PER_SEC;
> +		usecs = nsecs / NSECS_PER_USEC;
> +	}
> +
> +   	evname = __event_name(attr->type, attr->config);
> +	if  (!evname)
> +		evname = "(unknown)";
> +
> +	comm = al.thread->comm_set ? al.thread->comm : "-";
> +
> +	if (attr->sample_type & PERF_SAMPLE_CPU)
> +		cpu = sample->cpu;
> +
> +	if (symbol_conf.use_callchain && sample->callchain) {
> +
> +		if (perf_session__resolve_callchain(session, al.thread,
> +						sample->callchain, NULL) != 0) {
> +			if (verbose)
> +				error("Failed to resolve callchain. Skipping\n");
> +			return;
> +		}
> +
> +		node = session->callchain_cursor.first;
> +		if (!node)
> +			return;
> +
> +		while (node) {
> +			if (node->sym && node->sym->name)
> +				symname = node->sym->name;
> +			else if (show_unresolved)
> +				symname = "";
> +			else
> +				goto next;
> +
> +			if (node->map && node->map->dso && node->map->dso->name)
> +				dsoname = node->map->dso->name;
> +			else if (show_unresolved)
> +				dsoname = "";
> +			else
> +				goto next;
> +
> +			print_one_symbol(comm, al.thread->pid, cpu, secs, usecs,
> +			             evname, node->ip, symname, dsoname);
> +
> +next:
> +			prev = node;
> +			node = node->next;

Hmm, that's a wrong way of walking through callchains. In fact it's not
a classical list. node->next can be a ghost entry from a previous callchain
that we kept cached in order to optimize allocations.

You need the accessors callchain_cursor_current() and callchain_cursor_advance().
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