linux-kernel - Re: Mainline kernel OLTP performance update

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Date:	Wed, 6 May 2009 11:24:08 -0700
From:	Anirban Chakraborty <anirban.chakraborty@...gic.com>
To:	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>,
	"Styner, Douglas W" <douglas.w.styner@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	"Tripathi, Sharad C" <sharad.c.tripathi@...el.com>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"Kleen, Andi" <andi.kleen@...el.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Ma, Chinang" <chinang.ma@...el.com>,
	"Wang, Peter Xihong" <peter.xihong.wang@...el.com>,
	"Nueckel, Hubert" <hubert.nueckel@...el.com>,
	"Recalde, Luis F" <luis.f.recalde@...el.com>,
	"Nelson, Doug" <doug.nelson@...el.com>,
	"Cheng, Wu-sun" <wu-sun.cheng@...el.com>,
	"Prickett, Terry O" <terry.o.prickett@...el.com>,
	"Shunmuganathan, Rajalakshmi" <rajalakshmi.shunmuganathan@...el.com>,
	"Garg, Anil K" <anil.k.garg@...el.com>,
	"Chilukuri, Harita" <harita.chilukuri@...el.com>,
	"chris.mason@...cle.com" <chris.mason@...cle.com>
Subject: Re: Mainline kernel OLTP performance update




On 5/6/09 11:12 AM, "Wilcox, Matthew R" <matthew.r.wilcox@...el.com> wrote:

> That's a more accurate simulation of our workload, but Anirban's setup doesn't
> have nearly as many spindles as ours, so he won't do as many IOPS and may not
> see the problem.
> 
I was getting an IOPS in the order of 46000, which was not too far from what
Doug was getting. Orion settings indeed have a cache cold setting
(specifying cache size as 0). The IO was done as 1k block size in sequential
mode to the raw devices.
I can have that many luns but the issue is that Orion does not support that
may devices and I do not have the source code for it.
Let me see if I can find some other tool.

-Anirban

> All I'm trying to do is get something that will show the problem on his setup,
> and I think sequential IO is going to be the right answer here.  I could
> easily be wrong.
> 
> Neither FIO nor dd is going to have the cache behaviour of the database (maybe
> Orion does?)  As far as I can tell, we come to the kernel cache-cold for every
> IO simply because the database uses as many cache entries as it can.  We could
> write a little program to just thrash through cachelines, or just run gcc at
> the same time as this -- apparently gcc will happily chew through all the
> cache it can too.
> 
>> -----Original Message-----
>> From: Styner, Douglas W
>> Sent: Wednesday, May 06, 2009 11:05 AM
>> To: Wilcox, Matthew R; Anirban Chakraborty; linux-kernel@...r.kernel.org
>> Cc: Tripathi, Sharad C; arjan@...ux.intel.com; Kleen, Andi; Siddha, Suresh
>> B; Ma, Chinang; Wang, Peter Xihong; Nueckel, Hubert; Recalde, Luis F;
>> Nelson, Doug; Cheng, Wu-sun; Prickett, Terry O; Shunmuganathan,
>> Rajalakshmi; Garg, Anil K; Chilukuri, Harita; chris.mason@...cle.com
>> Subject: RE: Mainline kernel OLTP performance update
>> 
>> Wilcox, Matthew R writes:
>>> I'm not sure that Orion is going to give useful results in your hardware
>>> setup.  I suspect you don't have enough spindles to get the IO rates that
>>> are required to see the problem.  How about doing lots of contiguous I/O
>>> instead?  Something as simple as:
>>> 
>>> for i in sda sdb sdc (repeat ad nauseam); do \
>>>     dd if=/dev/$i of=/dev/null bs=4k iflag=direct & \
>>> done
>>> 
>> 
>> A better workload emulator would be to use FIO to generate ~60%/40%
>> reads/writes with ~90-95% random i/o using 2k blksize.  There is some
>> sequential writing in our workload but only to a log file and there is not
>> much activity there.

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