linux-kernel - Re: [PATCH v2 13/14] perf, persistent: Exposing persistent events using sysfs

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Date:	Fri, 14 Jun 2013 11:36:00 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Robert Richter <rric@...nel.org>
Cc:	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
	Robert Richter <robert.richter@...aro.org>
Subject: Re: [PATCH v2 13/14] perf, persistent: Exposing persistent events using sysfs

On Tue, 11 Jun 2013 18:42:39 +0200, Robert Richter wrote:
> From: Robert Richter <robert.richter@...aro.org>
>
> Expose persistent events in the system to userland using sysfs. Perf
> tools are able to read existing pmu events from sysfs. Now we use a
> persistent pmu as an event container containing all registered
> persistent events of the system. This patch adds dynamically
> registration of persistent events to sysfs. E.g. something like this:
>
>  /sys/bus/event_source/devices/persistent/events/mce_record:persistent,config=106
>  /sys/bus/event_source/devices/persistent/format/persistent:attr5:23
>
> Perf tools need to support the attr<num> syntax that is added in a
> separate patch set. With it we are able to run perf tool commands to
> read persistent events, e.g.:
>
>  # perf record -e persistent/mce_record/ sleep 10
>  # perf top -e persistent/mce_record/
>
> [ Document attr<index> syntax in sysfs ABI ]
> Reported-by: Jiri Olsa <jolsa@...hat.com>
> Signed-off-by: Robert Richter <robert.richter@...aro.org>
> Signed-off-by: Robert Richter <rric@...nel.org>
> ---
[SNIP]
> +static int pers_event_sysfs_register(struct pers_event *event)
> +{
> +	struct device_attribute *attr = &event->sysfs.attr;
> +	int idx;
> +
> +	*attr = (struct device_attribute)__ATTR(, 0444, pers_event_sysfs_show,
> +						NULL);
> +	attr->attr.name = event->name;

When I added another persistent event with this API, I got an WARNING
from lockdep like this:

[    0.432506] BUG: key ffff88040946f140 not in .data!
[    0.432581] ------------[ cut here ]------------
[    0.432656] WARNING: at /home/namhyung/project/linux/kernel/lockdep.c:2987 lockdep_init_map+0x53d/0x570()
[    0.432763] DEBUG_LOCKS_WARN_ON(1)


I guess we need the following line here:

	sysfs_attr_init(&attr->attr);


Thanks,
Namhyung


> +
> +	/* add sysfs attr to events: */
> +	for (idx = 0; idx < MAX_EVENTS; idx++) {
> +		if (!cmpxchg(persistent_events_attr + idx, NULL, &attr->attr))
> +			break;
> +	}
> +
> +	if (idx >= MAX_EVENTS)
> +		return -ENOSPC;
> +	if (!idx)
> +		EVENTS_GROUP = &persistent_events_group;
> +	if (!persistent_pmu.dev)
> +		return 0;	/* sysfs not yet initialized */
> +	if (idx)
> +		return sysfs_update_group(&persistent_pmu.dev->kobj,
> +					EVENTS_GROUP);
> +	return sysfs_create_group(&persistent_pmu.dev->kobj, EVENTS_GROUP);
> +}
>  
>  static int persistent_pmu_init(struct perf_event *event)
>  {
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