Re: hackbench regression since 2.6.25-rc

[Greg KH <gregkh@suse.de>]

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?

thanks,

greg k-h