linux-kernel - Re: [PATCH v3 1/9] smp: Run functions concurrently in smp_call_function

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Message-ID: <c02833c8-8c68-4331-03c7-d9e5eb2f285c@intel.com>
Date:   Fri, 19 Jul 2019 11:23:06 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Nadav Amit <namit@...are.com>, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Rik van Riel <riel@...riel.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v3 1/9] smp: Run functions concurrently in
 smp_call_function_many()

On 7/18/19 5:58 PM, Nadav Amit wrote:
> @@ -624,16 +622,11 @@ EXPORT_SYMBOL(on_each_cpu);
>  void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func,
>  			void *info, bool wait)
>  {
> -	int cpu = get_cpu();
> +	preempt_disable();
>  
> -	smp_call_function_many(mask, func, info, wait);
> -	if (cpumask_test_cpu(cpu, mask)) {
> -		unsigned long flags;
> -		local_irq_save(flags);
> -		func(info);
> -		local_irq_restore(flags);
> -	}
> -	put_cpu();
> +	__smp_call_function_many(mask, func, func, info, wait);
> +
> +	preempt_enable();
>  }

The get_cpu() was missing it too, but it would be nice to add some
comments about why preempt needs to be off.  I was also thinking it
might make sense to do:

	cfd = get_cpu_var(cfd_data);
	__smp_call_function_many(cfd, ...);
	put_cpu_var(cfd_data);
	
instead of the explicit preempt_enable/disable(), but I don't feel too
strongly about it.