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Date: Fri, 11 Dec 2015 00:19:06 +0900
From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Jan Kara <jack@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Petr Mladek <pmladek@suse.cz>,
        KY Srinivasan <kys@microsoft.com>,
        Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [PATCH 6/7] printk: Avoid scheduling printing threads on the
 same CPU
Message-ID: <20151210151906.GE540@swordfish>
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>+static void distribute_printing_kthreads(void)
>+{
>+	int i;
>+	unsigned int cpus_per_thread;
>+	unsigned int cpu, seen_cpu;
>+
>+	for (i = 0; i < PRINTING_TASKS; i++)
>+		cpumask_clear(printing_kthread_mask[i]);
>+
>+	cpus_per_thread = DIV_ROUND_UP(num_online_cpus(), PRINTING_TASKS);
>+	seen_cpu = 0;
>+	for_each_online_cpu(cpu) {
>+		cpumask_set_cpu(cpu,
>+			printing_kthread_mask[seen_cpu / cpus_per_thread]);
>+		seen_cpu++;
>+	}
>+
>+	for (i = 0; i < PRINTING_TASKS; i++)
>+		if (!cpumask_empty(printing_kthread_mask[i]))
>+			set_cpus_allowed_ptr(printing_kthread[i],
>+					     printing_kthread_mask[i]);
>+}


I certainly understand what are you trying to do here, but I'm a bit concerned.
This may result in 'bad' affinities on big.LITTLE platforms, for example. So I
think that printk is not quite good place for that type of decisions. Just my 5
cents.

	-ss