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Message-ID: <56CD0E4A.9080804@huawei.com>
Date:	Wed, 24 Feb 2016 09:58:34 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
CC:	Alexei Starovoitov <ast@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Cody P Schafer <dev@...yps.com>,
	"David S. Miller" <davem@...emloft.net>,
	He Kuang <hekuang@...wei.com>,
	Jérémie Galarneau 
	<jeremie.galarneau@...icios.com>, Jiri Olsa <jolsa@...nel.org>,
	Kirill Smelkov <kirr@...edi.com>,
	Li Zefan <lizefan@...wei.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>, <pi3orama@....com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/48] perf tools: Introduce bpf-output event



On 2016/2/24 1:45, Arnaldo Carvalho de Melo wrote:
> Em Mon, Feb 22, 2016 at 09:10:37AM +0000, Wang Nan escreveu:
>> Commit a43eec304259a6c637f4014a6d4767159b6a3aa3 (bpf: introduce
>> bpf_perf_event_output() helper) add a helper to enable BPF program
>> output data to perf ring buffer through a new type of perf event
>> PERF_COUNT_SW_BPF_OUTPUT. This patch enable perf to create perf
>> event of that type. Now perf user can use following cmdline to
>> receive output data from BPF programs:
>>
>>   # ./perf record -a -e bpf-output/no-inherit,name=evt/ \
>>                      -e ./test_bpf_output.c/map:channel.event=evt/ ls /
>>   # ./perf script
>>              perf  1560 [004] 347747.086295:                       evt:  ffffffff811fd201 sys_write ...
>>              perf  1560 [004] 347747.086300:                       evt:  ffffffff811fd201 sys_write ...
>>              perf  1560 [004] 347747.086315:                       evt:  ffffffff811fd201 sys_write ...
>>              ...
>>
>> Test result:
>>   # cat ./test_bpf_output.c
>>   /************************ BEGIN **************************/
>>   #include <uapi/linux/bpf.h>
>>   struct bpf_map_def {
>>   	unsigned int type;
>>   	unsigned int key_size;
>>   	unsigned int value_size;
>>   	unsigned int max_entries;
>>   };
>>
>>   #define SEC(NAME) __attribute__((section(NAME), used))
>>   static u64 (*ktime_get_ns)(void) =
>>   	(void *)BPF_FUNC_ktime_get_ns;
>>   static int (*trace_printk)(const char *fmt, int fmt_size, ...) =
>>   	(void *)BPF_FUNC_trace_printk;
>>   static int (*get_smp_processor_id)(void) =
>>   	(void *)BPF_FUNC_get_smp_processor_id;
>>   static int (*perf_event_output)(void *, struct bpf_map_def *, int, void *, unsigned long) =
>>   	(void *)BPF_FUNC_perf_event_output;
>>
>>   struct bpf_map_def SEC("maps") channel = {
>>   	.type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
>>   	.key_size = sizeof(int),
>>   	.value_size = sizeof(u32),
>>   	.max_entries = __NR_CPUS__,
>>   };
>>
>>   SEC("func_write=sys_write")
>>   int func_write(void *ctx)
>>   {
>>   	struct {
>>   		u64 ktime;
>>   		int cpuid;
>>   	} __attribute__((packed)) output_data;
>>   	char error_data[] = "Error: failed to output: %d\n";
>>
>>   	output_data.cpuid = get_smp_processor_id();
>>   	output_data.ktime = ktime_get_ns();
>>   	int err = perf_event_output(ctx, &channel, get_smp_processor_id(),
>>   				    &output_data, sizeof(output_data));
>>   	if (err)
>>   		trace_printk(error_data, sizeof(error_data), err);
>>   	return 0;
>>   }
>>   char _license[] SEC("license") = "GPL";
>>   int _version SEC("version") = LINUX_VERSION_CODE;
>>   /************************ END ***************************/
>>
>>   # ./perf record -a -e bpf-output/no-inherit,name=evt/ \
>>                      -e ./test_bpf_output.c/map:channel.event=evt/ ls /
>>   # ./perf script | grep ls
>>            ls  2242 [003] 347851.557563:                       evt:  ffffffff811fd201 sys_write ...
>>            ls  2242 [003] 347851.557571:                       evt:  ffffffff811fd201 sys_write ...
> So, there is something strange here:
>
>          if (unlikely(event->oncpu != smp_processor_id()))
>                  return -EOPNOTSUPP;
>
> This is where I am hitting, with:
>
> [acme@...et linux]$ uname -r
> 4.5.0-rc4
>
>          int err = perf_event_output(ctx, &channel, get_smp_processor_id(),
>                                      &output_data, sizeof(output_data));
>          if (err)
>                  trace_printk(error_data, sizeof(error_data), err);
>
> And then:
>
> [root@...et bpf]# tail /sys/kernel/debug/tracing/trace
>              perf-13040 [003] d... 12062.807729: : Error: failed to output: -95
>              perf-13040 [003] d... 12062.807731: : Error: failed to output: -95
>              perf-13040 [003] d... 12062.807732: : Error: failed to output: -95
>              perf-13040 [003] d... 12062.807735: : Error: failed to output: -95
>              perf-13040 [003] d... 12062.807737: : Error: failed to output: -95
>              perf-13040 [003] d... 12062.807744: : Error: failed to output: -95
>   gnome-terminal--3091  [001] d... 12062.807773: : Error: failed to output: -95
>   gnome-terminal--3091  [001] d... 12062.807784: : Error: failed to output: -95
>             gmain-2830  [002] d... 12062.811791: : Error: failed to output: -95
>             gmain-2830  [002] d... 12062.811810: : Error: failed to output: -95
> [root@...et bpf]#
>
> Ideas? AFK for a while, will continue investigating.

I also noticed this output, but didn't digg into it because all events
I concerned is okay. I'll look into this today.

> This already was submitted to Ingo, BTW.
>
> I used, as in the changeset comment tests:
>
> perf record -a -e bpf-output/no-inherit,name=evt/ -e ./test_bpf_output.c/map:channel.event=evt/ ls /
>
> And perf script told me:
>
> [root@...et bpf]# perf script | tail
>      perf 13040 [003] 12062.708337:  evt:  ffffffff81234eb1 sys_write (/lib/modules/4.5.0-rc4/build/vmlinux)
>      perf 13040 [003] 12062.708339:  evt:  ffffffff81234eb1 sys_write (/lib/modules/4.5.0-rc4/build/vmlinux)
>      perf 13040 [003] 12062.708340:  evt:  ffffffff81234eb1 sys_write (/lib/modules/4.5.0-rc4/build/vmlinux)
>      perf 13040 [003] 12062.708341:  evt:  ffffffff81234eb1 sys_write (/lib/modules/4.5.0-rc4/build/vmlinux)
>      perf 13040 [003] 12062.708343:  evt:  ffffffff81234eb1 sys_write (/lib/modules/4.5.0-rc4/build/vmlinux)
>      perf 13040 [003] 12062.708344:  evt:  ffffffff81234eb1 sys_write (/lib/modules/4.5.0-rc4/build/vmlinux)
>      perf 13040 [003] 12062.708346:  evt:  ffffffff81234eb1 sys_write (/lib/modules/4.5.0-rc4/build/vmlinux)
>      perf 13040 [003] 12062.708347:  evt:  ffffffff81234eb1 sys_write (/lib/modules/4.5.0-rc4/build/vmlinux)
>      perf 13040 [003] 12062.708348:  evt:  ffffffff81234eb1 sys_write (/lib/modules/4.5.0-rc4/build/vmlinux)
>      perf 13040 [003] 12062.708350:  evt:  ffffffff81234eb1 sys_write (/lib/modules/4.5.0-rc4/build/vmlinux)
> [root@...et bpf]#
>
> Wonder where that /lib/modules/4.5.0-rc4/build/vmlinux came from...
>
> [root@...et bpf]# perf script | cut -d'(' -f2 | sort | uniq -c
>     1141 /lib/modules/4.5.0-rc4/build/vmlinux)

It's a standard directory for perf searching vmlinux. Isn't it?

tools/perf/util/symbol.c:

static const char * const vmlinux_paths_upd[] = {
         "/boot/vmlinux-%s",
         "/usr/lib/debug/boot/vmlinux-%s",
         "/lib/modules/%s/build/vmlinux",
         "/usr/lib/debug/lib/modules/%s/vmlinux",
         "/usr/lib/debug/boot/vmlinux-%s.debug"
};

So what's your problem?

Thank you.

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