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Date: Thu, 1 Oct 2026 17:43:33 +0200
From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Ian Rogers <irogers@google.com>
Cc: Namhyung Kim <namhyung@kernel.org>, Aaron Tomlin <atomlin@atomlin.com>,
	Howard Chu <howardchu95@gmail.com>, Jakub Brnak <jbrnak@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Jiri Olsa <jolsa@kernel.org>,
	Adrian Hunter <adrian.hunter@intel.com>,
	James Clark <james.clark@linaro.org>,
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 15/26] perf trace: Filter the target's tasks in BPF
Message-ID: <ar5_pbVm1WYiq8Bg@x2>
References: <cover.1790145937.git.irogers@google.com>
 <20260928182605.3649015-1-irogers@google.com>
 <20260928182605.3649015-16-irogers@google.com>
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In-Reply-To: <20260928182605.3649015-16-irogers@google.com>

On Mon, Sep 28, 2026 at 11:25:54AM -0700, Ian Rogers wrote:
> +static bool task_traced(void)
> +{
> +	u64 pid_tgid = bpf_get_current_pid_tgid();
> +	pid_t pid = uses_tgid ? pid_tgid >> 32 : (pid_t)pid_tgid;
> +	bool *traced;
> +
> +	if (!has_pids_to_trace)
> +		return true;
> +

I didn't look at the generated code, some optimization may well make the
bpf_get_current_pif_tgid() to be executed only if has_pids_to_trace is
!NULL, otherwise it would be better to move that to after the test.

I'm applying it anyway, just caught my attention while applying.

- Arnaldo

> +	traced = bpf_map_lookup_elem(&pids_to_trace, &pid);
> +	return traced && *traced;
> +}