Date: Mon, 11 May 2015 10:31:50 -0400
From: Tejun Heo <tj@kernel.org>
To: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/5] workqueue: merge the similar code
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Hello, Lai.

On Mon, May 11, 2015 at 05:35:49PM +0800, Lai Jiangshan wrote:
> @@ -3440,48 +3440,86 @@ static struct pool_workqueue *alloc_unbound_pwq(struct workqueue_struct *wq,
>  }
>  
>  /**
> - * wq_calc_node_mask - calculate a wq_attrs' cpumask for the specified node
> - * @attrs: the wq_attrs of the default pwq of the target workqueue
> + * alloc_node_unbound_pwq - allocate a pwq for specified node

                                              for the specified node

> + * @wq: the target workqueue
> + * @dfl_pwq: the allocated default pwq
> + * @numa: NUMA affinity
>   * @node: the target NUMA node
> - * @cpu_going_down: if >= 0, the CPU to consider as offline
> - * @cpumask: outarg, the resulting cpumask
> + * @cpu_off: if >= 0, the CPU to consider as offline

@cpu_off sounds like offset into cpu array or sth.  Is there a reason
to change the name?

> + * @use_dfl_when_fail: use the @dfl_pwq in case the normal allocation failed

@use_dfl_on_fail

> + *
> + * Allocate or reuse a pwq with the cpumask that @wq should use on @node.

I wonder whether a better name for the function would be sth like
get_alloc_node_unbound_pwq().

>   *
> - * Calculate the cpumask a workqueue with @attrs should use on @node.  If
> - * @cpu_going_down is >= 0, that cpu is considered offline during
> - * calculation.  The result is stored in @cpumask.
> + * If NUMA affinity is not enabled, @dfl_pwq is always used.  @dfl_pwq
> + * was allocated with the effetive attrs saved in @dfl_pwq->pool->attrs.

I'm not sure we need the second sentence.

...
> - * Return: %true if the resulting @cpumask is different from @attrs->cpumask,
> - * %false if equal.
> + * Return: valid pwq, it might be @dfl_pwq under some conditions
> + * 		or might be the old pwq of the @node.
> + * 	   NULL, when the normal allocation failed.

Maybe explain how @use_dfl_on_fail affects the result?

>   */
> -static bool wq_calc_node_cpumask(const struct workqueue_attrs *attrs, int node,
> -				 int cpu_going_down, cpumask_t *cpumask)
> +static struct pool_workqueue *
> +alloc_node_unbound_pwq(struct workqueue_struct *wq,
> +		       struct pool_workqueue *dfl_pwq, bool numa,
> +		       int node, int cpu_off, bool use_dfl_when_fail)
> +
>  {
> -	if (!wq_numa_enabled || attrs->no_numa)
> +	struct pool_workqueue *pwq = unbound_pwq_by_node(wq, node);
> +	struct workqueue_attrs *attrs = dfl_pwq->pool->attrs, *tmp_attrs;
> +	cpumask_t *cpumask;
> +
> +	lockdep_assert_held(&wq_pool_mutex);
> +
> +	if (!wq_numa_enabled || !numa)
>  		goto use_dfl;
>  
> +	/*
> +	 * We don't wanna alloc/free wq_attrs for each call.  Let's use a
> +	 * preallocated one.  It is protected by wq_pool_mutex.
> +	 * tmp_attrs->cpumask will be updated in next and tmp_attrs->no_numa

                              will be updated below

> +	 * is not used, so we just need to initialize tmp_attrs->nice;
> +	 */
> +	tmp_attrs = wq_update_unbound_numa_attrs_buf;
> +	tmp_attrs->nice = attrs->nice;
> +	cpumask = tmp_attrs->cpumask;
> +
>  	/* does @node have any online CPUs @attrs wants? */
>  	cpumask_and(cpumask, cpumask_of_node(node), attrs->cpumask);
> -	if (cpu_going_down >= 0)
> -		cpumask_clear_cpu(cpu_going_down, cpumask);
> -
> +	if (cpu_off >= 0)
> +		cpumask_clear_cpu(cpu_off, cpumask);
>  	if (cpumask_empty(cpumask))
>  		goto use_dfl;
>  
> -	/* yeap, return possible CPUs in @node that @attrs wants */
> +	/* yeap, use possible CPUs in @node that @attrs wants */
>  	cpumask_and(cpumask, attrs->cpumask, wq_numa_possible_cpumask[node]);
> -	return !cpumask_equal(cpumask, attrs->cpumask);
> +	if (cpumask_equal(cpumask, attrs->cpumask))
> +		goto use_dfl;
> +	if (pwq && wqattrs_equal(tmp_attrs, pwq->pool->attrs))
> +		goto use_existed;

		goto use_current;

Also, would it be difficult to put this in a separate patch?  This is
mixing code refactoring with behavior change.  Make both code paths
behave the same way first and then refactor?

> +
> +	/* create a new pwq */
> +	pwq = alloc_unbound_pwq(wq, tmp_attrs);
> +	if (!pwq && use_dfl_when_fail) {
> +		pr_warn("workqueue: allocation failed while updating NUMA affinity of \"%s\"\n",
> +			wq->name);
> +		goto use_dfl;

Does this need to be in this function?  Can't we let the caller handle
the fallback instead?

Thanks.

-- 
tejun
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