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

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Date:   Tue, 22 Jan 2019 20:44:49 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Song Liu <songliubraving@...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 Tue, Jan 22, 2019 at 07:24:43PM +0000, Song Liu wrote:
> 
> 
> > 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?

plese send it, thanks

jirka