linux-kernel - Re: [RFC 0/4] [RFC] slub: Fastpath optimization (especially for RT)

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Message-ID: <20141027075830.GF23379@js1304-P5Q-DELUXE>
Date:	Mon, 27 Oct 2014 16:58:30 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	akpm@...uxfoundation.org, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	linux-mm@...ck.org, penberg@...nel.org, iamjoonsoo@....com
Subject: Re: [RFC 0/4] [RFC] slub: Fastpath optimization (especially for RT)

On Fri, Oct 24, 2014 at 09:41:49AM -0500, Christoph Lameter wrote:
> > I found that you said retrieving tid first is sufficient to do
> > things right in old discussion. :)
> 
> Right but the tid can be obtained from a different processor.
> 
> 
> One other aspect of this patchset is that it reduces the cache footprint
> of the alloc and free functions. This typically results in a performance
> increase for the allocator. If we can avoid the page_address() and
> virt_to_head_page() stuff that is required because we drop the ->page
> field in a sufficient number of places then this may be a benefit that
> goes beyond the RT and CONFIG_PREEMPT case.

Yeah... if we can avoid those function calls, it would be good.

But, current struct kmem_cache_cpu occupies just 32 bytes on 64 bits
machine, and, that means just 1 cacheline. Reducing size of struct may have
no remarkable performance benefit in this case.

Thanks.
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