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Message-ID: <20120531173351.GP14515@aftab.osrc.amd.com>
Date: Thu, 31 May 2012 19:33:51 +0200
From: Borislav Petkov <bp@...64.org>
To: Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>,
Ingo Molnar <mingo@...e.hu>,
LKML <linux-kernel@...r.kernel.org>,
Borislav Petkov <borislav.petkov@....com>
Subject: Re: [PATCH 1/2] perf: Add persistent event facilities
On Fri, May 18, 2012 at 12:14:00PM +0200, Peter Zijlstra wrote:
> On Wed, 2012-03-21 at 15:34 +0100, Borislav Petkov wrote:
> > +int perf_add_persistent_on_cpu(int cpu, struct pers_event_desc *desc,
> > + struct dentry *dir, unsigned nr_pages)
>
> OK, so this creates an even and registers it somewhere in debugfs.
>
> - you allow an arbitrary place in debugfs; this might make finding them
> 'interesting'. Should we put them all in the same place?
>
> - persistent events created from userspace don't seem to get a debugfs
> entry and will be lost forever?
>
> In general I think a little more exploring of the semantics and
> ramifications might be in order.
Ok, how about the following. This is rough and not in any way ready - it
is supposed to feel out how you guys feel about it. Basically, it adds
another file in (debugfs)/tracing/events/<subsys>/<event_name>/ which
can be used for whatever.
In the persistent event case, I get this:
/mnt/dbg/tracing/events/mce/mce_record/
|-- enable
|-- filter
|-- format
|-- id
`-- pers
and 'pers' contains the file descriptor of the perf per-cpu buffer which
I can mmap in userspace. I can read that out later.
Other events can put other files in there containing other relevant
stuff for them.
The interface trace_add_file() is pretty generic (it can be done
even more so). It is not design-finished - it is only meant to show
the intent. Oh, and don't look at bob_add_trace_file() - it is a
quick'n'dirty hack for testing :-).
So, what do you guys think, Peter, Steven?
Thanks.
--
diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 176a939d1547..1c13fb5e9a50 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -222,6 +222,8 @@ struct ftrace_event_call {
#ifdef CONFIG_PERF_EVENTS
int perf_refcount;
struct hlist_head __percpu *perf_events;
+ /* persistent event filedes */
+ int pers_fd;
#endif
};
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 29111da1d100..57ad0fbe0aef 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -980,6 +980,29 @@ show_header(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
return r;
}
+static ssize_t
+event_pers_fd_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
+{
+ struct ftrace_event_call *call = filp->private_data;
+ struct trace_seq *s;
+ int r;
+
+ if (*ppos)
+ return 0;
+
+ s = kmalloc(sizeof(*s), GFP_KERNEL);
+ if (!s)
+ return -ENOMEM;
+
+ trace_seq_init(s);
+ trace_seq_printf(s, "%d\n", call->pers_fd);
+
+ r = simple_read_from_buffer(ubuf, cnt, ppos,
+ s->buffer, s->len);
+ kfree(s);
+ return r;
+}
+
static const struct seq_operations show_event_seq_ops = {
.start = t_start,
.next = t_next,
@@ -1058,6 +1081,12 @@ static const struct file_operations ftrace_show_header_fops = {
.llseek = default_llseek,
};
+static const struct file_operations ftrace_persistent_fops = {
+ .open = tracing_open_generic,
+ .read = event_pers_fd_read,
+ .llseek = default_llseek,
+};
+
static struct dentry *event_trace_events_dir(void)
{
static struct dentry *d_tracer;
@@ -1199,6 +1228,56 @@ event_create_dir(struct ftrace_event_call *call, struct dentry *d_events,
return 0;
}
+static int __trace_add_file(struct ftrace_event_call *call, const char *fname,
+ umode_t mode, const struct file_operations *fops)
+{
+ int ret = 0;
+ mutex_lock(&event_mutex);
+
+ if (!trace_create_file(fname, mode, call->dir, call, fops))
+ ret = -EINVAL;
+
+ mutex_unlock(&event_mutex);
+ return ret;
+}
+
+extern struct ftrace_event_call *__start_ftrace_events[];
+extern struct ftrace_event_call *__stop_ftrace_events[];
+
+#define for_each_event(event, start, end) \
+ for (event = start; \
+ (unsigned long)event < (unsigned long)end; \
+ event++)
+
+/*
+ * Assumptions:
+ * - event debugfs dir is already initialized
+ * - trace event is not declared in a module
+ */
+int trace_add_file(const char *dir_name, const char *fname, umode_t mode,
+ const struct file_operations *fops)
+{
+ struct ftrace_event_call *call;
+
+ if (!strlen(fname))
+ return -EINVAL;
+
+ list_for_each_entry(call, &ftrace_events, list) {
+ if (!strncmp(call->name, dir_name, strlen(dir_name)))
+ return __trace_add_file(call, fname, mode, fops);
+ }
+ return -EINVAL;
+}
+
+static __init int bob_add_trace_file(void)
+{
+ int ret = 0;
+
+ ret = trace_add_file("mce_record", "pers", 0444, &ftrace_persistent_fops);
+
+ return ret;
+}
+
static int
__trace_add_event_call(struct ftrace_event_call *call, struct module *mod,
const struct file_operations *id,
@@ -1292,11 +1371,6 @@ void trace_remove_event_call(struct ftrace_event_call *call)
mutex_unlock(&event_mutex);
}
-#define for_each_event(event, start, end) \
- for (event = start; \
- (unsigned long)event < (unsigned long)end; \
- event++)
-
#ifdef CONFIG_MODULES
static LIST_HEAD(ftrace_module_file_list);
@@ -1435,9 +1509,6 @@ static struct notifier_block trace_module_nb = {
.priority = 0,
};
-extern struct ftrace_event_call *__start_ftrace_events[];
-extern struct ftrace_event_call *__stop_ftrace_events[];
-
static char bootup_event_buf[COMMAND_LINE_SIZE] __initdata;
static __init int setup_trace_event(char *str)
@@ -1753,3 +1824,4 @@ static __init int event_trace_self_tests_init(void)
late_initcall(event_trace_self_tests_init);
#endif
+late_initcall(bob_add_trace_file);
--
Regards/Gruss,
Boris.
Advanced Micro Devices GmbH
Einsteinring 24, 85609 Dornach
GM: Alberto Bozzo
Reg: Dornach, Landkreis Muenchen
HRB Nr. 43632 WEEE Registernr: 129 19551
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