linux-kernel - Re: [RESEND] IOZone with transparent huge page cache

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Message-ID: <516C8B03.7040203@sr71.net>
Date:	Mon, 15 Apr 2013 16:19:31 -0700
From:	Dave Hansen <dave@...1.net>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RESEND] IOZone with transparent huge page cache

On 04/15/2013 11:17 AM, Kirill A. Shutemov wrote:
> I run iozone using mmap files (-B) with different number of threads.
> The test machine is 4s Westmere - 4x10 cores + HT.

How did you run this, exactly?  Which iozone arguments?  It was run on
ramfs, since that's the only thing that transparent huge page cache
supports right now?

> ** Initial writers **
> threads:	        1        2        4        8       16       32       64      128      256
> baseline:	  1103360   912585   500065   260503   128918    62039    34799    18718     9376
> patched:	  2127476  2155029  2345079  1942158  1127109   571899   127090    52939    25950
> speed-up(times):     1.93     2.36     4.69     7.46     8.74     9.22     3.65     2.83     2.77

I'm a _bit_ surprised that iozone scales _that_ badly especially while
threads<nr_cpus.  Is this normal for iozone?  What are the units and
metric there, btw?

> Minimal speed up is in 1-thread reverse readers - 23%.
> Maximal is 9.2 times in 32-thread initial writers. It's probably due
> batched radix tree insert - we insert 512 pages a time. It reduces
> mapping->tree_lock contention.

It might actually be interesting to see this at 10, 20, 40, 80, etc...
since that'll actually match iozone threads to CPU cores on your
particular system.
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