linux-kernel - Re: [PATCH 0/4] zsmalloc improvements

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Message-ID: <4FFDD12B.1050909@linux.vnet.ibm.com>
Date:	Wed, 11 Jul 2012 14:16:59 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Nitin Gupta <ngupta@...are.org>,
	Robert Jennings <rcj@...ux.vnet.ibm.com>, linux-mm@...ck.org,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] zsmalloc improvements

On 07/11/2012 02:03 AM, Minchan Kim wrote:
> Today, I tested zsmapbench in my embedded board(ARM).
> tlb-flush is 30% faster than copy-based so it's always not win.
> I think it depends on CPU speed/cache size.

After you pointed this out, I decided to test this on my
Raspberry Pi, the only ARM system I have that is open enough
for me to work with.

I pulled some of the cycle counting stuff out of
arch/arm/kernel/perf_event_v6.c.  I've pushed that code to
the github repo.

git://github.com/spartacus06/zsmapbench.git

My results were in agreement with your findings.  I got 2040
cycles/map for the copy method and 947 cycles/map for the
page-table method.  I think memory speed is playing a big
roll in the difference.

I agree that the page-table method should be restored since
the performance difference is so significant on ARM, a
platform that benefits a lot from memory compression IMHO.

Still, the question remains how to implement the selection
logic, since not all archs that support the page-table
method will necessarily perform better with it.

Thanks,
Seth

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