[v7,7/8] perf tools: Check write_backward during evlist config

Message ID 1465957415-83376-8-git-send-email-wangnan0@huawei.com
State New
Headers show

Commit Message

Wang Nan June 15, 2016, 2:23 a.m.
Before this patch, when using overwritable ring buffer on an old
kernel, error message is misleading:

 # ~/perf record -m 1 -e raw_syscalls:*/overwrite/ -a
 Error:
 The raw_syscalls:sys_enter event is not supported.

This patch output clear error message to tell user his/her kernel
is too old:

 # ~/perf record -m 1 -e raw_syscalls:*/overwrite/ -a
 Reading from overwrite event is not supported by this kernel
 Error:
 The raw_syscalls:sys_enter event is not supported.

Signed-off-by: Wang Nan <wangnan0@huawei.com>

Cc: He Kuang <hekuang@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
---
 tools/perf/util/evsel.c  | 17 +++++------------
 tools/perf/util/evsel.h  | 13 +++++++++++++
 tools/perf/util/record.c | 17 +++++++++++++++++
 3 files changed, 35 insertions(+), 12 deletions(-)

-- 
1.8.3.4

Comments

Wang Nan June 20, 2016, 4:09 a.m. | #1
On 2016/6/17 5:47, Arnaldo Carvalho de Melo wrote:
> Em Wed, Jun 15, 2016 at 02:23:34AM +0000, Wang Nan escreveu:

>> Before this patch, when using overwritable ring buffer on an old

>> kernel, error message is misleading:

>>

>>   # ~/perf record -m 1 -e raw_syscalls:*/overwrite/ -a

>>   Error:

>>   The raw_syscalls:sys_enter event is not supported.

>>

>> This patch output clear error message to tell user his/her kernel

>> is too old:

>>

>>   # ~/perf record -m 1 -e raw_syscalls:*/overwrite/ -a

>>   Reading from overwrite event is not supported by this kernel

>>   Error:

>>   The raw_syscalls:sys_enter event is not supported.

> So I went to see if exposing that missing_features struct outside

> evsel.c was strictly needed and found that we already have fallbacking

> for this feature (attr.write_backwards) i.e. if we set it and

> sys_perf_event_open() fails, we will check if we are asking the kernel

> for some attr. field that it doesn't supports, set that missing_features

> and try again.

>

> But the way this was done for attr.write_backwards was buggy, as we need

> to check features in the inverse order of their introduction to the

> kernel, so that a newer tool checks first the newest perf_event_attr

> fields, detecting that the older kernel doesn't have support for them.

> The patch that introduced write_backwards support ([1]) in perf_evsel__open()

> did this checking after all the other older attributes, wrongly.

>

> [1]: b90dc17a5d14 ("perf evsel: Add overwrite attribute and check write_backward")

>

> Also we shouldn't even try to call sys_perf_event_open if

> perf_missing_features.write_backward is true and evsel->overwrite is

> also true, the old code would check this only after successfully opening

> the fd, do it before the open loop.

>

> Please take a look at the following patch, see if it is sufficient for

> handling older kernels, probably we need to emit a message to the user,

> but that has to be done at the builtin- level, i.e. at the tool, i.e.

> perf_evsel_open__strerror() should have what it takes to figure out this

> extra error and provide/ a proper string, lemme add this to the patch...

> done, please check:

>

> write_backwards_fallback.patch:


[SNIP]

>   

> @@ -1496,7 +1493,10 @@ try_fallback:

>   	 * Must probe features in the order they were added to the

>   	 * perf_event_attr interface.

>   	 */


I read this comment but misunderstand. I thought 'order' means newest last.

Will try your patch. Thank you.

> -	if (!perf_missing_features.clockid_wrong && evsel->attr.use_clockid) {

> +	if (!perf_missing_features.write_backward && evsel->attr.write_backward) {

> +		perf_missing_features.write_backward = true;

> +		goto fallback_missing_features;

> +	} else if (!perf_missing_features.clockid_wrong && evsel->attr.use_clockid) {

>   		perf_missing_features.clockid_wrong = true;

>   		goto fallback_missing_features;

>   	} else if (!perf_missing_features.clockid && evsel->attr.use_clockid) {

> @@ -1521,10 +1521,6 @@ try_fallback:

>   			  PERF_SAMPLE_BRANCH_NO_FLAGS))) {

>   		perf_missing_features.lbr_flags = true;

>   		goto fallback_missing_features;

> -	} else if (!perf_missing_features.write_backward &&

> -			evsel->attr.write_backward) {

> -		perf_missing_features.write_backward = true;

> -		goto fallback_missing_features;

>   	}

>   

>   out_close:

> @@ -2409,6 +2405,8 @@ int perf_evsel__open_strerror(struct perf_evsel *evsel, struct target *target,

>   	"We found oprofile daemon running, please stop it and try again.");

>   		break;

>   	case EINVAL:

> +		if (evsel->overwrite && perf_missing_features.write_backward)

> +			return scnprintf(msg, size, "Reading from overwrite event is not supported by this kernel.");

>   		if (perf_missing_features.clockid)

>   			return scnprintf(msg, size, "clockid feature not supported.");

>   		if (perf_missing_features.clockid_wrong)

Patch

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index ef223c7..59a69bb 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -29,17 +29,7 @@ 
 #include "trace-event.h"
 #include "stat.h"
 
-static struct {
-	bool sample_id_all;
-	bool exclude_guest;
-	bool mmap2;
-	bool cloexec;
-	bool clockid;
-	bool clockid_wrong;
-	bool lbr_flags;
-	bool write_backward;
-} perf_missing_features;
-
+struct perf_missing_features perf_missing_features;
 static clockid_t clockid;
 
 static int perf_evsel__no_extra_init(struct perf_evsel *evsel __maybe_unused)
@@ -690,8 +680,11 @@  static void apply_config_terms(struct perf_evsel *evsel,
 	 * possible to set overwrite globally, without config
 	 * terms.
 	 */
-	if (evsel->overwrite)
+	if (evsel->overwrite) {
+		WARN_ONCE(perf_missing_features.write_backward,
+			  "Reading from overwrite event is not supported by this kernel\n");
 		attr->write_backward = 1;
+	}
 
 	/* User explicitly set per-event callgraph, clear the old setting and reset. */
 	if ((callgraph_buf != NULL) || (dump_size > 0) || max_stack) {
diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
index 55ff958..17e506a 100644
--- a/tools/perf/util/evsel.h
+++ b/tools/perf/util/evsel.h
@@ -11,6 +11,19 @@ 
 #include "cpumap.h"
 #include "counts.h"
 
+struct perf_missing_features {
+	bool sample_id_all;
+	bool exclude_guest;
+	bool mmap2;
+	bool cloexec;
+	bool clockid;
+	bool clockid_wrong;
+	bool lbr_flags;
+	bool write_backward;
+};
+
+extern struct perf_missing_features perf_missing_features;
+
 struct perf_evsel;
 
 /*
diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c
index 481792c..e3ab812 100644
--- a/tools/perf/util/record.c
+++ b/tools/perf/util/record.c
@@ -90,6 +90,11 @@  static void perf_probe_context_switch(struct perf_evsel *evsel)
 	evsel->attr.context_switch = 1;
 }
 
+static void perf_probe_write_backward(struct perf_evsel *evsel)
+{
+	evsel->attr.write_backward = 1;
+}
+
 bool perf_can_sample_identifier(void)
 {
 	return perf_probe_api(perf_probe_sample_identifier);
@@ -129,6 +134,17 @@  bool perf_can_record_cpu_wide(void)
 	return true;
 }
 
+static void perf_check_write_backward(void)
+{
+	static bool checked = false;
+
+	if (!checked) {
+		perf_missing_features.write_backward =
+			!perf_probe_api(perf_probe_write_backward);
+		checked = true;
+	}
+}
+
 void perf_evlist__config(struct perf_evlist *evlist, struct record_opts *opts,
 			 struct callchain_param *callchain)
 {
@@ -136,6 +152,7 @@  void perf_evlist__config(struct perf_evlist *evlist, struct record_opts *opts,
 	bool use_sample_identifier = false;
 	bool use_comm_exec;
 
+	perf_check_write_backward();
 	/*
 	 * Set the evsel leader links before we configure attributes,
 	 * since some might depend on this info.