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Date: Mon, 9 Oct 2017 17:40:56 +0200
From: Jan Kara <jack@suse.cz>
To: Waiman Long <longman@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>, Jan Kara <jack@suse.com>,
        Jeff Layton <jlayton@poochiereds.net>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Tejun Heo <tj@kernel.org>,
        Christoph Lameter <cl@linux-foundation.org>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andi Kleen <andi@firstfloor.org>,
        Dave Chinner <dchinner@redhat.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [PATCH v7 4/6] lib/dlock-list: Make sibling CPUs share the same
 linked list
Message-ID: <20171009154056.GP17917@quack2.suse.cz>
References: <1507229008-20569-1-git-send-email-longman@redhat.com>
 <1507229008-20569-5-git-send-email-longman@redhat.com>
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On Thu 05-10-17 14:43:26, Waiman Long wrote:
> The dlock list needs one list for each of the CPUs available. However,
> for sibling CPUs, they are sharing the L2 and probably L1 caches
> too. As a result, there is not much to gain in term of avoiding
> cacheline contention while increasing the cacheline footprint of the
> L1/L2 caches as separate lists may need to be in the cache.
> 
> This patch makes all the sibling CPUs share the same list, thus
> reducing the number of lists that need to be maintained in each
> dlock list without having any noticeable impact on performance. It
> also improves dlock list iteration performance as fewer lists need
> to be iterated.
> 
> Signed-off-by: Waiman Long <longman@redhat.com>

...

> @@ -118,7 +156,7 @@ bool dlock_lists_empty(struct dlock_list_heads *dlist)
>  {
>  	int idx;
>  
> -	for (idx = 0; idx < nr_cpu_ids; idx++)
> +	for (idx = 0; idx < nr_dlock_lists; idx++)
>  		if (!list_empty(&dlist->heads[idx].list))
>  			return false;
>  	return true;
> @@ -207,7 +245,7 @@ struct dlock_list_node *__dlock_list_next_list(struct dlock_list_iter *iter)
>  	/*
>  	 * Try next list
>  	 */
> -	if (++iter->index >= nr_cpu_ids)
> +	if (++iter->index >= nr_dlock_lists)
>  		return NULL;	/* All the entries iterated */
>  
>  	if (list_empty(&iter->head[iter->index].list))

Why these two do not need a similar treatment as alloc_dlist_heads()?

								Honza

-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR