linux-kernel - Re: [PATCH v2 1/3] lib/list_batch: A simple list insertion/deletion batching facility

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Date:	Sun, 7 Feb 2016 10:57:44 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Waiman Long <waiman.long@....com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Andi Kleen <andi@...stfloor.org>,
	Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>
Subject: Re: [PATCH v2 1/3] lib/list_batch: A simple list insertion/deletion
 batching facility

On Wed, Feb 03, 2016 at 06:11:56PM -0500, Waiman Long wrote:
> On 01/31/2016 07:47 PM, Dave Chinner wrote:
> >So at what point does simply replacing the list_head with a list_lru
> >become more efficient than this batch processing (i.e.
> >https://lkml.org/lkml/2015/3/10/660)?  The list_lru isn't a great
> >fit for the inode list (doesn't need any of the special LRU/memcg
> >stuff https://lkml.org/lkml/2015/3/16/261) but it will tell us if,
> >like Ingo suggested, moving more towards a generic per-cpu list
> >would provide better overall performance...
> 
> I will take a look at the list_lru patch to see if that help. As for
> the per-cpu list, I tried that and it didn't quite work out.

OK, see my last email as to why Andi's patch didn't change anything.
The list_lru implementation has a list per node, a lock per node,
and each item is placed on the list for the node it is physically
allocated from. Hence for local workloads, the list/lock that is
accessed for add/remove should be local to the node and hence should
reduce cache line contention mostly to within a single node.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com