linux-kernel - Re: Mainline kernel OLTP performance update

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Date:	Fri, 23 Jan 2009 10:40:09 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Matthew Wilcox <matthew@....cx>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	netdev@...r.kernel.org, sfr@...b.auug.org.au,
	matthew.r.wilcox@...el.com, chinang.ma@...el.com,
	linux-kernel@...r.kernel.org, sharad.c.tripathi@...el.com,
	arjan@...ux.intel.com, suresh.b.siddha@...el.com,
	harita.chilukuri@...el.com, douglas.w.styner@...el.com,
	peter.xihong.wang@...el.com, hubert.nueckel@...el.com,
	chris.mason@...cle.com, srostedt@...hat.com,
	linux-scsi@...r.kernel.org, andrew.vasquez@...gic.com,
	anirban.chakraborty@...gic.com, mingo@...e.hu
Subject: Re: Mainline kernel OLTP performance update

On Fri, 2009-01-23 at 16:30 +0800, Zhang, Yanmin wrote:
> > I assume binding the client and the server to different physical CPUs
> > also  means that the SKB is always allocated on CPU 1 and freed on CPU
> > 2? If so, we will be taking the __slab_free() slow path all the time on
> > kfree() which will cause cache effects, no doubt.
> > 
> > But there's another potential performance hit we're taking because the
> > object size of the cache is so big. As allocations from CPU 1 keep
> > coming in, we need to allocate new pages and unfreeze the per-cpu page.
> > That in turn causes __slab_free() to be more eager to discard the slab
> > (see the PageSlubFrozen check there).
> > 
> > So before going for cache profiling, I'd really like to see an oprofile
> > report. I suspect we're still going to see much more page allocator
> > activity
> Theoretically, it should, but oprofile doesn't show that.
> 
> > there than with SLAB or SLQB which is why we're still behaving
> > so badly here.
> 
> oprofile output with 2.6.29-rc2-slubrevertlarge:
> CPU: Core 2, speed 2666.71 MHz (estimated)
> Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (Unhalted core cycles) count 100000
> samples  %        app name                 symbol name
> 132779   32.9951  vmlinux                  copy_user_generic_string
> 25334     6.2954  vmlinux                  schedule
> 21032     5.2264  vmlinux                  tg_shares_up
> 17175     4.2679  vmlinux                  __skb_recv_datagram
> 9091      2.2591  vmlinux                  sock_def_readable
> 8934      2.2201  vmlinux                  mwait_idle
> 8796      2.1858  vmlinux                  try_to_wake_up
> 6940      1.7246  vmlinux                  __slab_free
> 
> #slaninfo -AD
> Name                   Objects    Alloc     Free   %Fast
> :0000256                  1643  5215544  5214027  94   0 
> kmalloc-8192                28  5189576  5189560   0   0 
                                                    ^^^^^^

This looks bit funny. Hmm.

> :0000168                  2631   141466   138976  92  28 
> :0004096                  1452    88697    87269  99  96 
> :0000192                  3402    63050    59732  89  11 
> :0000064                  6265    46611    40721  98  82 
> :0000128                  1895    30429    28654  93  32 


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