linux-kernel - Re: hackbench regression since 2.6.25-rc

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Message-Id: <20080313091921.834d2532.randy.dunlap@oracle.com>
Date:	Thu, 13 Mar 2008 09:19:21 -0700
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Greg KH <gregkh@...e.de>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Kay Sievers <kay.sievers@...y.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: hackbench regression since 2.6.25-rc

On Thu, 13 Mar 2008 08:14:13 -0700 Greg KH wrote:

> On Thu, Mar 13, 2008 at 03:46:57PM +0800, Zhang, Yanmin wrote:
> > Comparing with 2.6.24, on my 16-core tigerton, hackbench process mode has about
> > 40% regression with 2.6.25-rc1, and more than 20% regression with kernel
> > 2.6.25-rc4, because rc4 includes the reverting patch of scheduler load balance.
> > 
> > Command to start it.
> > #hackbench 100 process 2000
> > I ran it for 3 times and sum the values.
> > 
> > I tried to investiagte it by bisect.
> > Kernel up to tag 0f4dafc0563c6c49e17fe14b3f5f356e4c4b8806 has the 20% regression.
> > Kernel up to tag 6e90aa972dda8ef86155eefcdbdc8d34165b9f39 hasn't regression.
> > 
> > Any bisect between above 2 tags cause kernel hang. I tried to checkout to a point between
> > these 2 tags for many times manually and kernel always paniced.
> 
> Where is the kernel panicing?  The changeset right after the last one
> above: bc87d2fe7a1190f1c257af8a91fc490b1ee35954, is a change to efivars,
> are you using that in your .config?
> 
> > All patches between the 2 tags are on kobject restructure. I guess such restructure
> > creates more cache miss on the 16-core tigerton.
> 
> Nothing should be creating kobjects on a normal load like this, so a
> regression seems very odd.  Unless the /sys/kernel/uids/ stuff is
> triggering this?
> 
> Do you have a link to where I can get hackbench (google seems to find
> lots of reports with it, but not the source itself), so I can test to
> see if we are accidentally creating kobjects with this load?

The version that I see referenced most often (unscientifically :)
is somewhere under people.redhat.com/mingo/, like so:
http://people.redhat.com/mingo/cfs-scheduler/tools/hackbench.c


---
~Randy
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