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

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Date:   Thu, 15 Dec 2016 17:48:31 -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 14:00, Joe Stringer <joe@....org> wrote:
> 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

The full branch with this change (fast-forward from your tmp branch)
is available here:
https://github.com/joestringer/linux/tree/submit/libbpf_samples_v5

I tried running every selftest and BPF sample I could get my hands on;
there's one or two that I couldn't run, but seemed more to do with my
versions of TC/iproute and kernel config rather than libbpf changes.
Let me know if you see any further trouble.