Re: [PATCH v3] riscv: don't stop itself in smp_send_stop

From: Andreas Schwab <schwab@suse.de>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-riscv@lists.infradead.org
Subject: Re: [PATCH v3] riscv: don't stop itself in smp_send_stop
Date: Tue, 18 Dec 2018 09:50:49 +0100	[thread overview]
Message-ID: <mvmimzr43rq.fsf@suse.de> (raw)
In-Reply-To: <20181217183619.GA23353@infradead.org> (Christoph Hellwig's message of "Mon, 17 Dec 2018 10:36:19 -0800")

On Dez 17 2018, Christoph Hellwig <hch@infradead.org> wrote:

>>  void smp_send_stop(void)
>>  {
>> -	on_each_cpu(ipi_stop, NULL, 1);
>> +	unsigned long timeout;
>> +
>> +	if (num_online_cpus() > 1) {
>> +		cpumask_t mask;
>> +
>> +		cpumask_copy(&mask, cpu_online_mask);
>> +		cpumask_clear_cpu(smp_processor_id(), &mask);
>> +
>> +		if (system_state <= SYSTEM_RUNNING)
>> +			pr_crit("SMP: stopping secondary CPUs\n");
>> +		send_ipi_message(&mask, IPI_CPU_STOP);
>> +	}
>> +
>> +	/* Wait up to one second for other CPUs to stop */
>> +	timeout = USEC_PER_SEC;
>> +	while (num_online_cpus() > 1 && timeout--)
>> +		udelay(1);
>> +
>> +	if (num_online_cpus() > 1)
>> +		pr_warn("SMP: failed to stop secondary CPUs %*pbl\n",
>> +			cpumask_pr_args(cpu_online_mask));
>
> Given that this function doesn't mark the current CPU as not offline
> it seems we could just exit early for num_online_cpus() == 1?

So much for copying existing implementations.

The only difference it would make is two less calls to num_online_cpus
on a single cpu system.  Hardly worth it, IMHO.

Andreas.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
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