linux-kernel - RE: Mainline kernel OLTP performance update

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Date:	Wed, 29 Apr 2009 10:06:44 -0600
From:	"Wilcox, Matthew R" <matthew.r.wilcox@...el.com>
To:	"Styner, Douglas W" <douglas.w.styner@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"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

Is it possible that's simply 'oprofile has a 4% overhead'?

> -----Original Message-----
> From: Styner, Douglas W
> Sent: Wednesday, April 29, 2009 9:00 AM
> To: Andi Kleen; Andrew Morton
> Cc: linux-kernel@...r.kernel.org; Tripathi, Sharad C;
> arjan@...ux.intel.com; Wilcox, Matthew R; 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
> 
> What we showed was that vmstat and vtune agreed wrt system/user time.
> Oprofile is off by ~4% (4% too low for user. 4% too high for system)
> 
> >-----Original Message-----
> >From: Andi Kleen [mailto:andi@...stfloor.org]
> >Sent: Wednesday, April 29, 2009 1:28 AM
> >To: Andrew Morton
> >Cc: Styner, Douglas W; linux-kernel@...r.kernel.org; Tripathi, Sharad C;
> >arjan@...ux.intel.com; Wilcox, Matthew R; 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
> >
> >Andrew Morton <akpm@...ux-foundation.org> writes:
> >
> >>> ======oprofile CPU_CLK_UNHALTED for top 30 functions
> >>> Cycles% 2.6.24.2                   Cycles% 2.6.30-rc3
> >>> 74.8578 <database>                 69.1925 <database>
> >>
> >> ouch, that's a large drop in userspace CPU occupancy.  It seems
> >> inconsistent with the 1.91% above.
> >
> >That was determined to be an oprofile artifact/regression (see Doug's
> >other email+thread) The 2.6.30 oprofile seems to be less accurate than
> >the one in 2.6.24. Of course the question is if it can't get
> >the user space right, is the kernel data accurate. But I believe
> >Doug verified with vtune that the kernel data is roughly correct,
> >just user space profiling was slightly bogus (right, Doug, or
> >do I misrepresent that?)
> >
> >-Andi
> >
> >--
> >ak@...ux.intel.com -- Speaking for myself only.