linux-kernel - Re: [PATCH v11 perf, bpf-next 7/9] perf tools: synthesize PERF_RECORD

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Message-ID: <CF447261-1B9C-423B-9508-60B32EAC4A5C@fb.com>
Date:   Tue, 22 Jan 2019 19:24:43 +0000
From:   Song Liu <songliubraving@...com>
To:     Jiri Olsa <jolsa@...hat.com>
CC:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v11 perf, bpf-next 7/9] perf tools: synthesize
 PERF_RECORD_* for loaded BPF programs



> On Jan 22, 2019, at 11:15 AM, Jiri Olsa <jolsa@...hat.com> wrote:
> 
> On Tue, Jan 22, 2019 at 06:38:56PM +0000, Song Liu wrote:
> 
> SNIP
> 
>>>> in perf_session__process_event, this happens right when processing
>>>> buildids in 'perf record', and also in 'perf report', so that is
>>>> something badly synthesized that hits perf.data for PERF_RECORD_KSYMBOL.
>>> 
>>> it's reproducible with simple:
>>> perf record -e cycles,instructions ls
>>> 
>>> as you said on irc, it's the machine->id_hdr_size size missing
>>> there's one more glitch, attached patch fixes that for me
>>> you can't use sizeof(struct ksymbol_event), because it includes
>>> the name as well.. which screws the size
>>> 
>>> but I don't know that code that much.. might be still something
>>> missing
>>> 
>>> jirka
>> 
>> Hi Arnaldo and Jiri,
>> 
>> Thanks for catching and fixing the bug. 
>> 
>> I guess the following is OK?
>> 
>>        *bpf_event = (struct bpf_event){
>>                .header = {
>>                        .type = PERF_RECORD_BPF_EVENT,
>>                        .size = sizeof(struct bpf_event),
>>                },
>>                .type = PERF_BPF_EVENT_PROG_LOAD,
>>                .flags = 0,
>>                .id = info.id,
>>        };
>> 
>> as struct bpf_event doesn't have variable length name:
>> 
>>        struct bpf_event {
>>                struct perf_event_header header;
>>                u16 type;
>>                u16 flags;
>>                u32 id;
>> 
>>                /* for bpf_prog types */
>>                u8 tag[BPF_TAG_SIZE];  // prog tag
>>        };
>> 
>> Or we need similar fix? 
> 
> yep, looks good.. also don't forget to add the 'machine->id_hdr_size'
> 
> jirka

So we still need something like?

diff --git i/tools/perf/util/bpf-event.c w/tools/perf/util/bpf-event.c
index 01e1dc1bb7fb..d7bf45485820 100644
--- i/tools/perf/util/bpf-event.c
+++ w/tools/perf/util/bpf-event.c
@@ -4,6 +4,7 @@
 #include <bpf/bpf.h>
 #include <bpf/btf.h>
 #include <linux/btf.h>
+#include "machine.h"
 #include "bpf-event.h"
 #include "debug.h"
 #include "symbol.h"
@@ -187,7 +188,7 @@ static int perf_event__synthesize_one_bpf_prog(struct perf_tool *tool,
                *bpf_event = (struct bpf_event){
                        .header = {
                                .type = PERF_RECORD_BPF_EVENT,
-                               .size = sizeof(struct bpf_event),
+                               .size = sizeof(struct bpf_event) + machine->id_hdr_size,
                        },
                        .type = PERF_BPF_EVENT_PROG_LOAD,
                        .flags = 0,

Would you send the official patch? Or would you prefer me sending it?

Thanks,
Song