linux-kernel - Re: [PATCH 6/6] IA64-sn2_smp: Combine two seq_printf() calls into one call in sn2_ptc_seq

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Date:   Sat, 22 Oct 2016 13:07:36 -0700
From:   Joe Perches <joe@...ches.com>
To:     SF Markus Elfring <elfring@...rs.sourceforge.net>,
        linux-ia64@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        Borislav Petkov <bp@...e.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hans-Christian Noren Egtvedt <egtvedt@...fundet.no>,
        Ingo Molnar <mingo@...nel.org>,
        Jörg Rödel <jroedel@...e.de>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Robert Richter <rrichter@...ium.com>,
        Robin Murphy <robin.murphy@....com>,
        Tony Luck <tony.luck@...el.com>,
        Toshi Kani <toshi.kani@....com>,
        Vineet Gupta <vgupta@...opsys.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 6/6] IA64-sn2_smp: Combine two seq_printf() calls into
 one call in sn2_ptc_seq_show()

On Sat, 2016-10-22 at 21:58 +0200, SF Markus Elfring wrote:
> Some data were printed into a sequence by two separate function calls.
> Print the same data by a single function call instead.
[]
> diff --git a/arch/ia64/sn/kernel/sn2/sn2_smp.c b/arch/ia64/sn/kernel/sn2/sn2_smp.c
[]
> @@ -494,12 +494,11 @@ static int sn2_ptc_seq_show(struct seq_file *file, void *data)
>  	int cpu;
>  
>  	cpu = *(loff_t *) data;
> -
> -	if (!cpu) {
> +	if (!cpu)
>  		seq_printf(file,
> -			   "# cpu ptc_l newrid ptc_flushes nodes_flushed deadlocks lock_nsec shub_nsec shub_nsec_max not_my_mm deadlock2 ipi_fluches ipi_nsec\n");
> -		seq_printf(file, "# ptctest %d, flushopt %d\n", sn2_ptctest, sn2_flush_opt);
> -	}
> +			   "# cpu ptc_l newrid ptc_flushes nodes_flushed deadlocks lock_nsec shub_nsec shub_nsec_max not_my_mm deadlock2 ipi_fluches ipi_nsec\n"
> +			   "# ptctest %d, flushopt %d\n",
> +			   sn2_ptctest, sn2_flush_opt);
>  
>  	if (cpu < nr_cpu_ids && cpu_online(cpu)) {
>  		stat = &per_cpu(ptcstats, cpu);

Please think more.

printf has to inspect character by character looking for
a vsprintf % character and 0 termination.

seq_puts does a strlen then memcpy.

Which is faster?
When is it better to call 2 functions?
When does readability matter more than efficiency?