linux-kernel - Re: [PATCH v2] uprobes: make trace_uprobe->nhit counter a per-CPU one

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Message-ID: <20240813145002.GB31977@redhat.com>
Date: Tue, 13 Aug 2024 16:50:03 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Andrii Nakryiko <andrii@...nel.org>
Cc: linux-trace-kernel@...r.kernel.org, rostedt@...dmis.org,
	mhiramat@...nel.org, peterz@...radead.org, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org, jolsa@...nel.org
Subject: Re: [PATCH v2] uprobes: make trace_uprobe->nhit counter a per-CPU one

On 08/09, Andrii Nakryiko wrote:
>
> @@ -815,13 +824,21 @@ static int probes_profile_seq_show(struct seq_file *m, void *v)
>  {
>  	struct dyn_event *ev = v;
>  	struct trace_uprobe *tu;
> +	unsigned long nhits;
> +	int cpu;
>
>  	if (!is_trace_uprobe(ev))
>  		return 0;
>
>  	tu = to_trace_uprobe(ev);
> +
> +	nhits = 0;
> +	for_each_possible_cpu(cpu) {
> +		nhits += READ_ONCE(*per_cpu_ptr(tu->nhits, cpu));

why not

		nhits += per_cpu(*tu->nhits, cpu);

?

See for example per_cpu_sum() or nr_processes(), per_cpu() should work just fine...

Other than that

Reviewed-by: Oleg Nesterov <oleg@...hat.com>