RE: Mainline kernel OLTP performance update

[Wilcox, Matthew R]

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@xxxxxxxxxxxxxxx; Tripathi, Sharad C;
> arjan@xxxxxxxxxxxxxxx; 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@xxxxxxxxxx
> 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@xxxxxxxxxxxxxx]
> >Sent: Wednesday, April 29, 2009 1:28 AM
> >To: Andrew Morton
> >Cc: Styner, Douglas W; linux-kernel@xxxxxxxxxxxxxxx; Tripathi, Sharad C;
> >arjan@xxxxxxxxxxxxxxx; 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@xxxxxxxxxx
> >Subject: Re: Mainline kernel OLTP performance update
> >
> >Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx -- Speaking for myself only.
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