Re: [PATCH bpf-next v2 2/2] bpftool: Add misc secion and probe for large INSN limit

From: Quentin Monnet <quentin.monnet@netronome.com>
To: Michal Rostecki <mrostecki@opensuse.org>
Cc: bpf@vger.kernel.org, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>, Andrii Nakryiko <andriin@fb.com>,
	Jakub Kicinski <jakub.kicinski@netronome.com>,
	Stanislav Fomichev <sdf@google.com>,
	Peter Wu <peter@lekensteyn.nl>,
	Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH bpf-next v2 2/2] bpftool: Add misc secion and probe for large INSN limit
Date: Wed, 8 Jan 2020 15:28:30 +0000	[thread overview]
Message-ID: <091b68b1-d651-6b23-c3d7-7334ccde1700@netronome.com> (raw)
In-Reply-To: <20200108134148.GD2954@wotan.suse.de>

2020-01-08 13:41 UTC+0000 ~ Michal Rostecki <mrostecki@opensuse.org>
> On Tue, Jan 07, 2020 at 02:36:15PM +0000, Quentin Monnet wrote:
>> Nit: typo in subject ("secion").
>>
>> 2020-01-07 14:03 UTC+0100 ~ Michal Rostecki <mrostecki@opensuse.org>
>>> Introduce a new probe section (misc) for probes not related to concrete
>>> map types, program types, functions or kernel configuration. Introduce a
>>> probe for large INSN limit as the first one in that section.
>>>
>>> Signed-off-by: Michal Rostecki <mrostecki@opensuse.org>
>>> ---
>>>  tools/bpf/bpftool/feature.c | 18 ++++++++++++++++++
>>>  1 file changed, 18 insertions(+)
>>>
>>> diff --git a/tools/bpf/bpftool/feature.c b/tools/bpf/bpftool/feature.c
>>> index 03bdc5b3ac49..d8ce93092c45 100644
>>> --- a/tools/bpf/bpftool/feature.c
>>> +++ b/tools/bpf/bpftool/feature.c
>>> @@ -572,6 +572,18 @@ probe_helpers_for_progtype(enum bpf_prog_type prog_type, bool supported_type,
>>>  		printf("\n");
>>>  }
>>>  
>>> +static void
>>> +probe_large_insn_limit(const char *define_prefix, __u32 ifindex)
>>> +{
>>> +	bool res;
>>> +
>>> +	res = bpf_probe_large_insn_limit(ifindex);
>>> +	print_bool_feature("have_large_insn_limit",
>>> +			   "Large complexity and program size limit",
>>
>> I am not sure we should mention "complexity" here. Although it is
>> related to program size in the kernel commit you describe, the probe
>> that is run is only on instruction number. This can make a difference
>> for offloaded programs: When you probe a device, if kernel has commit
>> c04c0d2b968a and supports up to 1M instructions, but hardware supports
>> no more than 4k instructions, you may still benefit from the new value
>> for BPF_COMPLEXITY_LIMIT_INSNS for complexity, but not for the total
>> number of available instructions. In that case the probe will fail, and
>> the message on complexity would not be accurate.
>>
>> Looks good otherwise, thanks Michal!
>>
>> Quentin
> 
> Thanks for review! Should I change the description just to "Large
> program size limit" or "Large instruction limit"?
> 
> Michal
> 

I don't really have a preference here, let's keep "program size"?
Quentin