linux-kernel - Re: [PATCH perf/core REBASE 2/5] samples/bpf: Switch over to libbpf

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Message-ID: <CAPWQB7GhHZOf4c5mu=__mNNyFFeq+jOZMawweMBg=sNiPpt-zg@mail.gmail.com>
Date:   Thu, 15 Dec 2016 14:00:48 -0800
From:   Joe Stringer <joe@....org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, Wang Nan <wangnan0@...wei.com>,
        ast@...com, Daniel Borkmann <daniel@...earbox.net>,
        Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH perf/core REBASE 2/5] samples/bpf: Switch over to libbpf

On 15 December 2016 at 10:34, Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> Em Thu, Dec 15, 2016 at 03:29:18PM -0300, Arnaldo Carvalho de Melo escreveu:
>> Em Thu, Dec 15, 2016 at 12:50:22PM -0300, Arnaldo Carvalho de Melo escreveu:
>> > Em Wed, Dec 14, 2016 at 02:43:39PM -0800, Joe Stringer escreveu:
>> > > Now that libbpf under tools/lib/bpf/* is synced with the version from
>> > > samples/bpf, we can get rid most of the libbpf library here.
>> > >
>> > > Signed-off-by: Joe Stringer <joe@....org>
>> > > Cc: Alexei Starovoitov <ast@...com>
>> > > Cc: Daniel Borkmann <daniel@...earbox.net>
>> > > Cc: Wang Nan <wangnan0@...wei.com>
>> > > Link: http://lkml.kernel.org/r/20161209024620.31660-6-joe@ovn.org
>> > > [ Use -I$(srctree)/tools/lib/ to support out of source code tree builds, as noticed by Wang Nan ]
>>
>> So, the above comment no longer applied to this adjusted patch from you,
>> as you removed one hunk too much, that, after applied, gets samples/bpf/
>> to build successfully:
>>
>> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
>> index add514e2984a..81b0ef2f7994 100644
>> --- a/samples/bpf/Makefile
>> +++ b/samples/bpf/Makefile
>> @@ -107,6 +107,7 @@ always += lwt_len_hist_kern.o
>>  always += xdp_tx_iptunnel_kern.o
>>
>>  HOSTCFLAGS += -I$(objtree)/usr/include
>> +HOSTCFLAGS += -I$(srctree)/tools/lib/
>>  HOSTCFLAGS += -I$(srctree)/tools/testing/selftests/bpf/
>>
>>  HOSTCFLAGS_bpf_load.o += -I$(objtree)/usr/include -Wno-unused-variable
>>
>> ---------------------
>>
>> I added it, continuing...
>
> But then, when I tried to run offwaketime with it, it fails:
>
> [root@...et bpf]# ./offwaketime  ls
> bpf_load_program() err=22
> BPF_LDX uses reserved fields
> bpf_load_program() err=22
> BPF_LDX uses reserved fields
> [root@...et bpf]#
>
> If I remove this patch and try again, it works:
>
> [root@...et bpf]# ./offwaketime | head -4
> swapper/1;start_secondary;cpu_startup_entry;schedule_preempt_disabled;schedule;__schedule;-;---;; 46
> chrome;return_from_SYSCALL_64;do_syscall_64;exit_to_usermode_loop;schedule;__schedule;-;try_to_wake_up;do_futex;sys_futex;do_syscall_64;return_from_SYSCALL_64;;Chrome_ChildIOT 1
> firefox;entry_SYSCALL_64_fastpath;sys_poll;do_sys_poll;poll_schedule_timeout;schedule_hrtimeout_range;schedule_hrtimeout_range_clock;schedule;__schedule;-;try_to_wake_up;pollwake;__wake_up_common;__wake_up_sync_key;pipe_write;__vfs_write;vfs_write;sys_write;entry_SYSCALL_64_fastpath;;Timer 3
> dockerd-current;entry_SYSCALL_64_fastpath;sys_select;core_sys_select;do_select;poll_schedule_timeout;schedule_hrtimeout_range;schedule_hrtimeout_range_clock;schedule;__schedule;-;try_to_wake_up;futex_wake;do_futex;sys_futex;entry_SYSCALL_64_fastpath;;dockerd-current 2
> [root@...et bpf]#
>
>
> So, I'm stopping here so that I can push what I have to Ingo, then I'll get
> back to this, hopefully by then you beat me and I have just to retest 8-)

OK, thanks for the report. Looks like there was another difference
between the two libbpfs - one used total program size for its
load_program API; the actual kernel API uses instruction count. This
incremental should do the trick:

https://github.com/joestringer/linux/commit/6ff7726f20077bed66fb725f5189c13690154b6a