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Date: Wed, 24 Jun 2026 12:24:31 -0700
From: Namhyung Kim <namhyung@kernel.org>
To: Viktor Malik <vmalik@redhat.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	linux-perf-users@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@kernel.org>, Ian Rogers <irogers@google.com>,
	Adrian Hunter <adrian.hunter@intel.com>,
	James Clark <james.clark@linaro.org>,
	Howard Chu <howardchu95@gmail.com>, linux-kernel@vger.kernel.org,
	bpf@vger.kernel.org, Michael Petlan <mpetlan@redhat.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH] perf trace: Refactor augmented_raw_syscalls using
 bpf_loop
Message-ID: <ajwu7xR6V6MAQOFw@google.com>
References: <20260623112533.1151502-1-vmalik@redhat.com>
 <DJGJ9F6WQZV9.2W4WBIHYLJQ97@gmail.com>
 <ajq98dm4gAwEzkMb@google.com>
 <c2f4e45e-d5c9-42e9-a46b-25fb0cacb267@redhat.com>
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In-Reply-To: <c2f4e45e-d5c9-42e9-a46b-25fb0cacb267@redhat.com>

On Wed, Jun 24, 2026 at 08:47:38AM +0200, Viktor Malik wrote:
> On 6/23/26 19:10, Namhyung Kim wrote:
> > Hello,
> > 
> > On Tue, Jun 23, 2026 at 08:27:39AM -0700, Alexei Starovoitov wrote:
> >> On Tue Jun 23, 2026 at 4:25 AM PDT, Viktor Malik wrote:
[SNIP]
> >>> +	struct args_loop_ctx loop_ctx = {
> >>> +		.args = args,
> >>> +		.beauty_map = beauty_map,
> >>> +		.payload_offset = payload_offset,
> >>> +		.value_size = value_size,
> >>> +		.output = &output,
> >>> +		.do_output = &do_output
> >>> +	};
> >>> +	iters = bpf_loop(6, process_arg_cb, &loop_ctx, 0);
> >>
> >> bpf_loop() is old and generally not recommended.
> >> Please use bpf_for() then the diff will be one line change and
> >> can scale to any number of args. Not just 6.
> 
> Thanks Alexei, I didn't know about this preference.
> 
> > One thing we should take care is to support old kernels.  The oldest
> > LTS kernel in the kernel.org is 5.10 and bpf_loop() was introduced in
> > 5.17 and bpf_for (bpf_iter_num) was 6.4.
> 
> The problematic loop was introduced in 6.12 by a68fd6a6cdd3 ("perf
> trace: Collect augmented data using BPF") so we should be good using
> bpf_for. Or is perf from 7.2 supposed to work on 5.10 LTS kernels?

Yep, we'd like to support old kernels.

Thanks,
Namhyung