linux-kernel - Re: [RFC PATCH 03/14] tracing/filters: Enable filtering a scalar field by a cpumask

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Message-ID: <20230705150013.5ba7ddb8@gandalf.local.home>
Date:   Wed, 5 Jul 2023 15:00:13 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Valentin Schneider <vschneid@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, kvm@...r.kernel.org, linux-mm@...ck.org,
        bpf@...r.kernel.org, x86@...nel.org,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Juerg Haefliger <juerg.haefliger@...onical.com>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Nadav Amit <namit@...are.com>,
        Dan Carpenter <error27@...il.com>,
        Chuang Wang <nashuiliang@...il.com>,
        Yang Jihong <yangjihong1@...wei.com>,
        Petr Mladek <pmladek@...e.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>, Song Liu <song@...nel.org>,
        Julian Pidancet <julian.pidancet@...cle.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Dionna Glaze <dionnaglaze@...gle.com>,
        Thomas Weißschuh <linux@...ssschuh.net>,
        Juri Lelli <juri.lelli@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Yair Podemsky <ypodemsk@...hat.com>
Subject: Re: [RFC PATCH 03/14] tracing/filters: Enable filtering a scalar
 field by a cpumask

On Wed,  5 Jul 2023 19:12:45 +0100
Valentin Schneider <vschneid@...hat.com> wrote:

> +/* Optimisation of do_filter_cpumask() for scalar values */
> +static inline int
> +do_filter_cpumask_scalar(int op, unsigned int cpu, const struct cpumask *mask)
> +{
> +	switch (op) {
> +	case OP_EQ:
> +		return cpumask_equal(mask, cpumask_of(cpu));
> +	case OP_NE:
> +		return !cpumask_equal(mask, cpumask_of(cpu));

The above two can be optimized much more if the cpu is a scalar. If mask is
anything but a single CPU, then EQ will always be false, and NE will always
be true. If the mask contains a single CPU, then we should convert the mask
into the scalar CPU and just do:

	case OP_EQ:
		return mask_cpu == cpu;
	case op_NE:
		return maks_cpu != cpu;

-- Steve

> +	case OP_BAND:
> +		return cpumask_test_cpu(cpu, mask);
> +	default:
> +		return 0;
> +	}
> +}