linux-kernel - Re: hackbench regression due to commit 9dfc6e68bfe6e

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Date:	Fri, 26 Mar 2010 10:35:02 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Ma, Ling" <ling.ma@...el.com>,
	"Zhang, Yanmin" <yanmin.zhang@...el.com>,
	"Chen, Tim C" <tim.c.chen@...el.com>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: hackbench regression due to commit 9dfc6e68bfe6e

On Thu, 2010-03-25 at 22:49 +0800, Christoph Lameter wrote:
> On Thu, 25 Mar 2010, Alex Shi wrote:
> 
> >     SLUB: Use this_cpu operations in slub
> >
> > The hackbench is prepared hundreds pair of processes/threads. And each
> > of pair of processes consists of a receiver and a sender. After all
> > pairs created and ready with a few memory block (by malloc), hackbench
> > let the sender do appointed times sending to receiver via socket, then
> > wait all pairs finished. The total sending running time is the indicator
> > of this benchmark. The less the better.
> 
> > The socket send/receiver generate lots of slub alloc/free. slabinfo
> > command show the following slub get huge increase from about 81412344 to
> > 141412497, after command "backbench 150 thread 1000" running.
> 
> The number of frees is different? From 81 mio to 141 mio? Are you sure it
> was the same load?
The slub free number has similar increase, the following is the data
before testing:
name                   Objects      Alloc       Free   %Fast Fallb Onn
:t-0001024                 855   81412344   81411981  93   1     0 3
:t-0000256                1540   81224970   81223835  93   1     0 1

I am sure there is no effective task running when I do testing. 

Just for this info, CONFIG_SLUB_STATS enabled.

> 
> > Name                   Objects      Alloc       Free   %Fast Fallb O
> > :t-0001024                 870  141412497  141412132  94   1     0 3
> > :t-0000256                1607  141225312  141224177  94   1     0 1
> >
> >
> > Via perf tool I collected the L1 data cache miss info of comamnd:
> > "./hackbench 150 thread 100"
> >
> > On 33-rc1, about 1303976612 time L1 Dcache missing
> >
> > On 9dfc6, about 1360574760 times L1 Dcache missing
> 
> I hope this is the same load?
for the same load parameter: ./hackbench 150 thread 1000
on 33-rc1, about 10649258360 times L1 Dcache missing
on 9dfc6, about 11061002507 times L1 Dcahce missing

For this this info, without CONFIG_SLUB_STATS and slub_debug is close. 

> 
> What debugging options did you use? We are now using per cpu operations in
> the hot paths. Enabling debugging for per cpu ops could decrease your
> performance now. Have a look at a dissassembly of kfree() to verify that
> there is no instrumentation.
> 
Basically, slub_debug never opened in booting, some SLUB related kernel
config is here:
CONFIG_SLUB_DEBUG=y
CONFIG_SLUB=y
#CONFIG_SLUB_DEBUG_ON is not set

I just dissemble kfree, but whether the KMEMTRACE enabled or not, the
trace_kfree code stay in kfree function, and in my testing the debugfs
are not mounted.  

> 

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